Research Progress on Application in Energy Conversion of Silicon Carbide-Based Catalyst Carriers

Abstract

In modern industrial production, heterogeneous catalysts play an important role. A catalyst carrier, as a constituent of heterogeneous catalysts, is employed for supporting and loading active components. The catalyst carrier has a considerable impact on the overall acting performance of the catalysts in actual production. Therefore, a catalyst carrier should have some necessary properties such as a high specific surface area, excellent mechanical strength and wear resistance, and better thermal stability. Among the candidate materials, silicon carbide (SiC) has excellent physical and chemical properties due to its special crystal structure; these properties include outstanding thermal conductivity and remarkable mechanical strength and chemical stability. Therefore, SiC materials with a high specific surface area basically meet the requirements of catalyst carriers. Accordingly, SiC has broad application prospects in the field of catalysis and is an ideal material for preparing catalyst carriers. In the present study, we reviewed the preparation methods and the variation in the raw materials used for preparing SiC-based catalyst carriers with high specific surface areas, in particular the research progress on the application of SiC-based catalyst carriers in the field of energy-conversion in recent years. The in-depth analysis indicated that the construction of SiC with a special structure, large-scale synthesis of SiC by utilizing waste materials, low-temperature synthesis of SiC, and exploring the interaction between SiC supports and active phases are the key strategies for future industrial development; these will have far-reaching significance in enhancing catalytic efficiency, reutilization of resources, ecological environmental protection, energy savings, and reductions in energy consumption.

1. Introduction

Most reaction processes need to be completed through heterogeneous catalytic reactions in the energy-conversion process. Catalysis is the foundation of modern chemical industries, and the application of catalysts in chemical industry production is of significance in both industrial development and social progress. The catalyst carrier that constitutes a heterogeneous catalyst is used to support catalytically active components, but the industrial production conditions are relatively harsh and changeable. Therefore, the catalyst carrier must meet the requirements of a high specific surface area, excellent mechanical strength and wear resistance, and high acid/alkali resistance and thermal stability.

Being indispensable in actual industrial production, catalysts are composed of specific active components that play a major catalytic role and carriers that support the active components. As mentioned above, the performance of the carrier itself considerably affects the catalytic performance of the active components in reactions. SiC, incidentally discovered by Acheson in an experiment [1], has a structure similar to that of diamond and belongs to atomic crystals. A unit cell of SiC consists of four carbon atoms and four silicon atoms, where one C atom and four Si atoms form a C-Si tetrahedral structure. Due to the stronger tetrahedral sp3 hybrid bond [2], SiC has excellent physical and chemical stability and other advantages that include outstanding thermal conductivity, excellent mechanical strength and wear resistance, and high chemical stability. Due to these remarkable properties, SiC is suitable for many reactions in harsh environments, and it has been widely used in various fields [2,3,4,5,6,7,8,9,10].

The intrinsic performance of SiC with an enhanced specific surface area meets the requirements of catalyst carriers. It is known that most of the chemical industry’s production is carried out under high-temperature and acid-base conditions as well as in large reactors. For conventional catalyst supports such as alumina, silica, and carbon, their disadvantages are gradually exaggerated as the actual production conditions become more and more severe. Carriers composed of alumina and silica have poor thermal conductivity and chemical stability. In addition, they are not resistant to acids and bases, which leads to a reduction in the surface area and a loss of active sites during the reaction process. A significant shortcoming of the catalysts with carbon carriers is that they are prone to oxidation and are not suitable for high-temperature production. Thus, it can be inferred that the traditional catalyst carriers cannot meet the requirements of production in chemical industries [2,3,4]. In contrast, SiC with excellent performance has an outstanding thermal conductivity in a high-temperature environment that dissipates the surface heat easily and allows the surface to be evenly heated. In addition, SiC has a higher mechanical strength and wear resistance, which allow it to withstand long-distance transportation and vigorous stirring in large reactors. Similarly, under other harsh reaction conditions, SiC can still maintain its original structure to support active components and complete catalytic tasks [11]. As a new catalyst carrier, SiC is gradually replacing traditional catalyst carriers in this field [12,13,14,15]. However, the specific surface area of a conventional SiC carrier is small (the specific surface area of a commercial SiC carrier is less than 1 m²/g [16,17,18]), due to which it cannot meet the requirement of supporting active components. Therefore, the production of SiC carriers with a high specific surface area has become the focus of the research field. In most of the previous related studies, researchers increased the specific surface area through a special preparation method of SiC to meet the requirements of catalysis. However, these preparation methods require high temperatures; there have been a few studies on the preparation of SiC carriers using waste as raw materials and at low temperatures. With the increase in the global resource crisis and the destruction of the ecological environment, the reuse of resources, energy savings and emission reductions, and ecological protection have increasingly become the development trends for industrial production. Therefore, exploring the low-temperature preparation of SiC carriers with a high specific surface area using waste will be the future direction of this field.

In this study, the preparation methods and applications of SiC materials reported in recent years were reviewed. Combined with the research work of this research group, the principles, advantages, and disadvantages of SiC materials as catalyst carriers in practical applications in the field of energy-conversion were analyzed. In addition, the future development of SiC-based catalyst carriers was foreseen.

2. Preparation and Raw Material Variation in Silicon Carbide (SiC)-Based Catalyst Carriers

At present, ordinary SiC has a small specific surface area that is not conducive to the dispersion of active components. In order to enhance the catalytic performance, SiC supports with a high specific surface area should be prepared by various means so that the loaded active components can be dispersed better. Due to the dispersion effect that results from the high specific surface area, the catalyst has more active sites, which can save a great deal of costs compared to increasing the amount of active sites by increasing the amount of active components. The current commonly used methods for preparing SiC with a high specific surface area are mainly carbothermic reduction and other strategies derived from this principle. We believe that the principle of obtaining a high specific surface area can be roughly divided into two types: one is to prepare SiC nanomaterials, and the other is to prepare porous SiC materials.

2.1. Carbothermic Reduction Method

Carbothermic reduction is the most common and efficient method for preparing SiC materials. The preparation process is generally carried out in an inert gas atmosphere, and SiC is obtained by mixing a carbon source and a silicon source at a high temperature. By varying the types and structures of carbon and silicon sources as well as the ratio of the two sources, SiC materials with different morphologies can be obtained. The mechanism of carbothermic reduction to produce SiC is as follows [19,20,21,22]:

SiO₂(s) + C(s) → SiO(g) + CO(g)

(1)

SiO(g) + C(s) → SiC(s) + CO(g)

(2)

SiO(g) + 3CO(g) → SiC(s) + 2CO₂(g)

(3)

CO₂(g) + C(s) → 2CO(g)

(4)

SiC nanofibers and particles can be produced by the carbothermic reduction method [19]. Nanomaterials have surface effects that manifest as a rapid increase in the specific surface area of the particles with the decrease in size. When the particle size reaches the nanometer scale, the surface atoms of the particles account for increasingly high percentages [23]. As catalyst carriers, SiC materials with a high specific surface area can be obtained through the preparation of SiC into nanoscale materials or through the direct preparation of nanoscale SiC materials.

The production process of nano-SiC can be divided into two stages: nucleation and growth [24]. First, SiO is mainly obtained by reaction (1), and it then reacts with solid carbon (2) to generate SiC nanoparticles (NPs) as “nuclei”. When the CO gas generated in the first two steps reaches saturation, SiO reacts with CO to form SiC nanofibers at the positions of the previously generated particles. Moreover, the reaction (4) also provides the CO gas required for reaction (3) to satisfy the requirement of a CO-saturated atmosphere.

Kudrenko et al. [25] adopted a carbon source (carbon fibers) with a certain structure to discuss the nucleation and growth situations of SiC nanowires on the surface of the carbon fibers. The surface was not smooth and was covered with spherical hillocks (carbon) with a diameter of 20–50 nm; these hillocks were randomly distributed on the surface of the carbon fibers. First, SiO₂ was reduced by C through a carbothermic reduction to form SiO and CO; second, SiO migrated onto the carbon fiber surfaces under the action of vapor and reacted with the hillocks on the surface to form SiC nanocrystals. The spherical hillock structures on the carbon fibers not only functioned as reducing agents, but also served as templates for forming SiC NPs. Although this reaction did not guarantee the growth of SiC nanowires [26], the obtained SiC nanocrystals could serve as crystal nuclei. Subsequently, nanowires grew via the reaction of SiO and CO in the saturated CO vapors. The (111) plane of SiC exhibited the lowest surface energy; therefore, most Si and C atoms migrated to the (111) plane [27,28]. The SiO and CO vapor reacted along the (111) direction and then formed nanowires [26].

Yao et al. [19] synthesized SiC nanostructures via the carbothermic reduction of a mesoporous carbon–silica (C-SiO₂) nanocomposite material. After removing the unreacted SiO₂ and C, the SiC nanocomposite material exhibited a larger specific surface area in the range of 76.7–83.0 m²/g. During the preparation process, the porosity of the precursor, the C/SiO₂ ratio, and the C-SiO₂ structure were the key factors. Accordingly, SiC with controllable nanostructures could be synthesized by simply varying these three structural factors. When the precursor had a higher C/SiO ratio (Figure 1a), the higher carbon content of the mesoporous pore’s wall resulted in higher partial pressures of SiO and CO. Because the pore channels were small, SiO and CO were hardly carried away from the mesoporous C-SiO₂ sample by argon passing through. As a result, they could form SiC nuclei in pores all around the precursor through the reaction SiO₂(s) + C(s) → SiO(g) + CO(g). Subsequently, SiC nanofibers were grown via the gas-phase reaction between SiO and CO on the surface of the mesoporous C-SiO₂ particles. In contrast, when the precursor had a lower C/SiO ratio (Figure 1b), the C-SiO₂ nanocomposites were infiltrated by a small amount of carbon, but the interface between the C/SiO₂ pore walls and carbon increased the local concentrations of SiO and CO significantly and decreased the partial pressure of oxygen gas. The locally concentrated SiO species readily reacted with carbon to generate a large amount of SiC nuclei in the entire mesoporous C-SiO₂ nanocomposite, and the subsequent reaction was consistent with the above-mentioned process except that a higher proportion of nanofibers was formed. The preparation of nano-SiC in this way can provide new insights for the formation of SiC nanostructures.

To prepare catalyst carriers for efficient methanol and ethanol electrooxidation, Dong et al. [29] adopted a carbothermic reduction to fabricate SiC/expanded graphite (EG) nanocomposites through EG via an SiC outer layer. As a result, the active components; i.e., Pt NPs, could be supported on the nanocomposite material to form a Pt/SiC/EG catalyst with a specific surface area up to 97.4 m²/g. The effects of Pt loaded on the SiC/EG and C (carbon) carriers on the electrooxidation of methanol and ethanol, respectively, were compared. The experimental results indicated that the performance of the Pt/SiC/EG catalyst was better than that of the Pt/C catalyst, which was because SiC as the “coating layer” endowed the entire SiC/EG carrier with a high chemical stability, a high corrosion resistance, and a porous network structure. The high chemical stability and corrosion resistance enabled the SiC/EG carrier to prevent the catalyst structure from being destroyed during the reaction. In addition, the porous network structure of the SiC/EG carrier could be interconnected and the active Pt NPs could be fully dispersed, which effectively prevented agglomeration.

At present, SiC nanomaterials are favored by many researchers as an ideal material for catalyst carriers. Due to the high specific surface area and excellent physical and chemical properties of the SiC nanomaterials prepared via carbothermic reduction, they exhibit remarkable performances when used as catalyst carriers. Chen et al. [30] prepared porous SiC nanowire scaffolds as catalyst carriers, and the prepared materials exhibited the characteristics of open pores, a low thermal conductivity, and chemical inertness. The added SiC nanowires and the directly created SiC nanostructures were used to build a porous model then reduce the brittleness of the material and increase the specific surface area of the material so they could be used as catalyst carriers. Dong et al. [31] also prepared SiC materials with a high surface area via carbothermic reduction and electrodeposited Pt NPs on the surface, due to which the active component Pt was fully dispersed and utilized. Furthermore, Dong et al. [29] studied the use of SiC-coated graphite nanocomposites as the carrier for NP catalysts for efficient electrooxidation of methanol and ethanol. The coated nanocomposites exhibited high specific surface areas and could better support the active components of the nanocatalysts; they also showed high thermal stability and chemical stability. Zhang et al. [32] prepared a spongy aerogel with a large number of interlaced SiC/Si3N4 nanowires as the skeleton. The material exhibited a remarkable performance as a catalyst carrier; furthermore, it also showed ultra-high porosity, ultra-low density, a large internal surface area, resistance to high temperatures, and stable chemical properties. The precursors, structures, quantitative preparation conditions, and specific surface areas of different nano-SiC materials are shown in

Table 1. Precursors, preparation conditions, structures, and specific surface areas of different nano-SiC materials.

Precursor	Temperature	Time	SiC Structure	SiC Specific Surface Area (m2/g)	Ref.
Mesoporous C-SiO2 nanocomposites	1450 °C	5 h	Nanofibers and nanoparticle	76.7–83.0	[19]
Expanded graphite (EG) and silica sol	1300 °C	6 h	Nanobelts	97.4	[29]
SiO2–sugar slurries	1500 °C	3 h	3D SiCNW scaffolds	-	[30]
Polymer sponge with reactive particles	1600 °C	3 h	3D porous structure with interwoven nanofibers	28.26	[32]

.

However, with the spread and acceptance of the “low-energy production” concept all over the world, the production of more valuable products with lower production costs and low energy consumption has become a powerful force to promote the development of “low-carbon industries”. Under normal circumstances, the temperature range required to prepare SiC via carbothermic reduction is around 1350–1500 °C, and the high temperature and high energy consumption do not meet the requirements of low-energy production. For the carbothermic reduction method to become the most important strategy to produce SiC, innovations in the production steps and preparation methods and obtaining the required SiC nanomaterials with low energy consumption are the future directions and trends in this field.

2.2. Other Methods

In order to prepare high-performance SiC with a high specific surface area, domestic and foreign researchers have improved and innovated the carbothermic reduction method. The modifications mainly focus around the mixing method of raw materials and the types and morphologies of the precursors so that the carbon source and the silicon source can be fully contacted or the prepared SiC has a special structure; this can lead to the formation of SiC with a high specific surface area.

2.2.1. Sol-Gel Method

SiC precursors are generally prepared by directly mixing carbon sources and silicon sources. In order to achieve a uniform mixing of silicon sources and carbon sources at the molecular level, the sol-gel method can be used to prepare precursors and then to obtain SiC via carbothermic reduction.

Jin et al. [33] first described a route to prepare mesoporous SiC via sol-gel. Tetraethyl orthosilicate (TEOS) and phenolic resin were used to prepare a binary carbonaceous silica xerogel. In this process, nickel nitrate was used as pore-adjusting agent. Mesoporous SiC was obtained via carbothermal reduction of the binary xerogel at 1250 °C, and its specific surface area could reach 112 m²/g; on this basis, Zheng et al. [34] further developed the sol-gel method and synthesized a new type of mesoporous SiC with a specific surface area of 141 m²/g via carbothermal reduction of a carbonaceous silica xerogel.

Since then, this method has been tried and improved. Li et al. [18] adopted the sol-gel method and the carbothermic reduction method to prepare SiC with a high specific surface area. They used citric acid as the pore-forming agent and ethyl silicate and phenolic resin as the raw materials to prepare nano-SiC powder at a high temperature of 1500 °C in an argon atmosphere. The specific surface area of the obtained nano-SiC powder could reach 62 m²/g. As mentioned above, due to the surface size effect and porous structure of the nano-SiC powder, it exhibited a considerably higher specific surface area compared with the conventional commercial SiC carrier (<1 m²/g) and therefore can be used as a better catalyst carrier in the field of catalysis.

Worsley et al. [35] prepared silica-coated carbon aerogels via the sol-gel method and obtained carbon-supported SiC aerogels with a high specific surface area after carbothermic reduction. The specific process involved the use of an activated carbon aerogel (ACA) with a specific surface area greater than 3000 m²/g as a carrier for silica sol-gel deposition to obtain a silica-coated carbon aerogel with a specific surface area greater than 2000 m²/g and remarkable thermal stability. Subsequently, in a flowing Ar atmosphere at 1500 °C, the silica-coated carbon aerogel underwent carbothermic reduction to form a carbon-supported SiC aerogel with a large specific surface area, and it could maintain an overall surface area greater than 2000 m²/g. As a new type of material with a high specific surface area and high temperature stability, the SiC/ACA material has very broad application prospects in the field of catalyst carriers.

Wang et al. [36] used polymethylhydrogensiloxane (PMHS) as a soft template to synthesize porous SiC with a high specific surface area of 125 m²/g via the sol-gel method. The main preparation process was as follows: PMHS was used as the pore regulator in the sol-gel process, and furfuryl alcohol and tetraethoxysilane were used as the carbon and silicon precursors, respectively, to prepare carbon-containing silica xerogels; then, in an inert atmosphere, SiC was obtained via high-temperature carbothermic reduction. As a byproduct of the silicon industry, PMHS is inexpensive, non-toxic, and stable in air and moisture. It can assemble itself into special conformations and form porous structures in xerogels; therefore, it has been applied as a structure-directing agent for the preparation of mesoporous silica materials [37]. The SiC material obtained in this process could partially inherit the porous structure of its xerogel’s precursor during carbothermic reduction; thus, it exhibited a high specific surface area and pore volume. Based on the sol-gel method and carbothermic reduction, other techniques can also be introduced to better synthesize the precursor gel so that the prepared SiC has better properties. For instance, Wu et al. [38] used a one-step sol-gel method combined with CO₂ supercritical drying technology to synthesize a novel catechol–formaldehyde/silica hybrid aerogel (CF/SiO₂) that they then converted to a C/SiO₂/SiC ternary aerogel via carbothermic reduction at 1500 °C in argon. The aerogel exhibited a large specific surface area (746.87 m²/g), a higher micropore volume (0.2279 cm³/g), and a higher porosity (89.10%). The use of this ternary aerogel as a catalyst carrier could lead to better dispersity of the active components, more active sites, and better overall performance of the catalyst. Due to the high stability of SiO₂ and SiC at high temperatures [39,40,41,42,43,44], the ternary aerogel was suitable for high-efficiency thermal insulation in inert and oxidizing atmospheres at high temperatures.

2.2.2. Shape Memory Synthesis (SMS)

SMS refers to using a carbon source or a silicon source with “structural template” characteristics to prepare SiC materials through carbothermic reduction in which the SiC maintains the structure and morphology of the raw material. This method was invented by Ledoux and his team [45,46]. When using this method to prepare SiC with a large surface area, a porous carbon source with a high specific surface area is usually used as the template so that the prepared SiC can inherit the special structure and surface morphology of the raw material.

Ledoux et al. [46] fully analyzed the feasibility and advantages of SiC as a catalyst carrier and compared it with other traditional catalyst carriers. The SiC-based catalyst carriers exhibited an excellent performance, a high thermal conductivity and mechanical strength, a strong oxidation resistance, etc.; therefore, they met the requirements of a good heterogeneous catalyst carrier. In general, catalysts with practical use are heterogeneous and consist of one or more active components and a carrier that provides a porous framework and a high specific surface area. These special surface structures allow reagents to come into contact with the active components. The high porosity and high specific surface area can result in better dispersion of the active phase and significant increase in the number of active sites. Dispersion increases the activity of a catalyst by increasing the number of active sites rather than the number of active phases.

In order to prepare SiC with a high specific surface area, Ledoux et al. [46] used the SMS method to make the obtained material retain the structural characteristics of the raw material with a high specific surface area. First, in a temperature range of 1280–1520 K, Si and SiO₂ were mixed and heated to generate SiO vapor, and then the SiO vapor was pumped to the position of the shaped carbon material (activated carbon or porous coke). The SiO reacted with C at a lower temperature (1280–1480 K) to form SiC; as mentioned above, this reaction also generated CO gas. The CO gas migrated into the reaction zone and reacted with SiO, due to which the equilibrium shifted to the direction of forming SiC. Finally, through surface nucleation and crystal growth, a SiC material with the same morphology as the raw material was obtained. Ledoux et al. [47] studied the effect of different preparation conditions on the synthesis of SiC with a high specific surface area. The main factors such as the preparation temperature, reaction time, and mass ratio of (Si + SiO₂)/C affected the formation rate, yield, and specific surface area of SiC. The study found that when the preparation temperature was higher (>1250 °C) and the reaction time was 15 h, more activated carbon could be converted into SiC, but its specific surface area was relatively low (20–50 m²/g); when the preparation temperature was lower (1200 °C), the mass ratio of (Si + SiO₂)/C was high, and the reaction time was 15 h, SiC with a larger specific surface area (40–50 m²/g) was obtained. In addition, Ledoux et al. [46] explored a further increase in the specific surface area of the SiC catalyst carrier mainly by impregnating some non-volatile elements such as U, Ce, and Zr on the activated carbon precursor to vary the physical and chemical properties of the obtained SiC carrier. The introduction of these elements could increase the specific surface area of the prepared SiC without carbon deposition on its surface; therefore, there was no need to clean up before the specific catalytic reaction.

The SMS method can be regarded as a type of template method, and the production of SiC nanomaterials using carbon fibers [25] as the carbon source, as mentioned above, is achieved by using carbon templates. The difference is that the former mainly involves inheriting the initial structure of the raw material, whereas the latter uses the special morphology of the carbon source to provide a more favorable growth basis for the SiC nanomaterials. The SMS method uses porous raw materials to prepare porous SiC carriers with a high specific surface area. The application of the SMS method has played a directional role in the synthesis of catalyst carriers. The research in this field can rely on this method for the innovation and preparation of new catalyst carriers suitable for application in various areas.

2.2.3. Nanocasting Method

The nanocasting method uses a material with a special pore structure as the template and introduces the precursor of the target material into it. Through the nanoconfining effect of the template material, the precursor reacts in situ to afford a SiC material with the desired structure [42,48,49].

Two types of templates are used in the nanocasting method: the hard template and the soft template. The hard template refers to a pre-prepared porous material. The precursor of the guest (target product) is filled in the pores of the main body of the original template. After the reaction, the target products can be obtained on the hard template [50] (as shown in Figure 2). The hard template can be regarded as a rigid structural framework with excellent mechanical properties, due to which it remains after the reaction and must be cleaned with acids or via other methods. Comparatively, the structure of a soft template is relatively soft and mainly consists of organic molecules or supramolecules; it has strong interactions with the precursors and also needs to be removed after obtaining the desired structure.

According to previously reported studies, the main template generally used for synthesizing nanoporous SiC is the SiO₂ template [48,49,51,52,53,54,55,56]. This method can be used to prepare porous SiC ceramics with a large surface area and numerous ordered internal pores. Porous SiC ceramics have the excellent properties of both porous ceramics and SiC such as resistance to high temperatures and thermal shock, wear resistance, and chemical stability [57]; therefore, they have been extensively used in chemical industries, energy, environmental protection, biomedicine, metallurgy, and military industries [58,59,60,61,62]. Porous SiC ceramics prepared via the nanocasting method have great advantages as catalyst carriers.

Hoffmann et al. [63] used porous glass as the template in the nanocasting method to prepare nanoporous SiC with a specific surface area as high as 477 m²/g. The first step was the synthesis of porous glass, which was then infiltrated with a liquid precursor of SiC using the nanocasting method. The siliceous material acted as a mold during the polymer-carbide transformation while pyrolyzing, after which the resultant product was etched with diluted hydrofluoric acid to obtain nanoporous SiC. In addition, the SiC product could retain the unique pore structure and particle morphology of the porous glass, which verified that the nanoscale structure could be maintained in the SiC products.

Lu et al. [64] used mesoporous silica SBA-15 as a nanoreactor and furfuryl alcohol as the carbon source and combined the nanocasting process with carbothermic reduction to produce mesoporous SiC with a high specific surface area of about 160 m²/g. Through this preparation method, while infiltrating into the channels of SBA-15, carbon can also infiltrate onto the silica walls where micropores exist, thereby forming periodic and nanoscale carbon and silica dispersions and consequently making the reaction more complete. It is worth noting that as one of the most widely used catalyst carriers [65,66,67], mesoporous silica has a regular pore structure and a high specific surface area, and the catalyst obtained from it has better active sites. However, the drawback of mesoporous silica materials is their poor stability at high temperatures, which limits their industrial applications [68,69]. Therefore, the SiC carrier prepared by using mesoporous silica as the nanoreactor not only has a porous structure, but also has the characteristics of SiC; i.e., a high temperature resistance and a good chemical stability.

Nardin et al. [70] used a new soft templating agent to prepare porous SiC in an oxygen- and moisture-free environment. They employed a solid network of semifluorinated alkanes (SFAs) as the template (SFAs form agglomerates or gels in oil [71,72,73,74,75]) and 1,3,5-trisilacyclohexane (TSCH), which is liquid at room temperature, as the molecular precursor. The network self-assembled in the immediate precursor (liquid), and the gel phase was converted into polysilanes through the polymerization of the TSCH molecules around the solid network of SFAs. After the SFAs were removed from the polysilanes via washing, it was calcined at 1000 °C in an argon atmosphere to be converted to SiC with high porosity. Furthermore, soluble directing agents that could self-agglomerate directly in liquid organosilanes to act as soft supramolecular templates were added [76]; if the supramolecular structure was maintained in the subsequent steps, the formation of porous SiC could be expected. After removing the polymeric organosilanes and the template from the obtained polymer, the product was pyrolyzed into SiC ceramics (Figure 3). The specific surface area of the porous SiC prepared via this method was in the range of 18–30 m²/g. Compared with the specific surface areas of the SiC carriers obtained via the first two methods using a hard template, the specific surface area of the SiC carrier prepared via the soft template method was smaller.

2.3. Raw Material Variation for SiC Preparation

Previously, the raw materials used for preparing SiC were conventional pure carbon sources and silicon sources; that is, the synthesis of SiC was carried out directly using pure carbon sources and silicon sources. In recent years, with the advancement of science and technology and the awareness of environmental protection, an increasing number of researchers have begun to pay attention to the raw materials used for synthesizing SiC and obtain carbon or silicon sources from recycled waste and garbage and then produce SiC materials with various structures and uses. The recycling of waste as the main method of resource reuse has great practical significance in environmental protection, energy conservation and emission reduction, and the development of a circular economy.

Meng et al. [77] used waste plastics, water bottles, and disposable boxes as carbon sources to prepare β-SiC nanomaterials with different sizes via a simple carbothermic reduction method. These wastes were carbonized and used as carbon sources; they were mixed with SiO₂ impregnated with Fe(NO₃)₃ and then reduced through carbothermic reduction to obtain SiC NPs. The sizes of the SiC NPs synthesized from water bottles and disposable boxes were mainly 5–20 nm and 30–70 nm, respectively. These extremely small NPs exhibited high specific surface areas due to the surface effect. In addition to the above-mentioned waste materials, disposable chopsticks are also one of the most common wastes in China’s daily life, but they are rich in carbon. If the discarded disposable chopsticks can be recycled, it can reduce the threat to the ecological environment and simultaneously help in “turning waste into treasure”. For instance, Wang Donghua [78] used discarded disposable chopsticks (convenient chopsticks) as the carbon source to prepare SiC and the silica sol obtained by the hydrolysis of ethyl orthosilicate as the silicon source. The waste disposable wooden chopsticks were ground into powder and added to the previously prepared silicon source together with Fe(NO₃)₃ to form a gel, then carbothermic reduction was carried out at 1300 °C. After the reaction, a SiC microtube composed of SiC NPs was obtained; the specific surface area of the SiC microtube was 37 m²/g. Maroufi et al. [24] used the glass part of discarded computer monitors as the silica source and the plastic casing of the computers as the carbon source to prepare three SiC nanowires with different morphologies in an inert atmosphere at 1550 °C. The BET analysis confirmed that the prepared SiC nanowires had mesoporous properties with a specific surface area of 51.4 m²/g. Compared with the specific surface area of the SiC prepared from pure raw materials mentioned above, the specific surface area of the SiC prepared from waste materials was smaller. Although the latter basically met the requirements of a catalyst carrier, its performance was worse than that of the former. Therefore, the use of waste to prepare SiC-based carriers with a larger specific surface area is still an issue that needs to be explored.

Furthermore, Qian et al. [79] invented a method for preparing cubic ultrafine SiC powder from waste plastic as the raw material at a low temperature; that is, they used waste plastic as the carbon source and synthesized SiC through the reaction of the carbon source and silicon powder. In this process, sodium and magnesium were used as the reducing agents, and sulfur powder was used as the auxiliary agent. These raw materials were reacted at 350–500 °C and 0.5–10 MPa for 10–30 h and then washed and purified to obtain SiC powder. This method not only reused waste but also afforded SiC at a low temperature, which not only reduced the cost of raw materials but also helped achieve energy savings and a reduction in energy consumption. However, the disadvantage of this method was that an extremely high pressure was required to synthesize SiC at a low temperature. We believe that with more exploration and research, the method of using waste to prepare SiC-based catalyst carriers with excellent performance at low temperatures can become the developmental direction of this field in the future. Moreover, it can also provide new ideas for ecological environmental protection and resource reuse.

3. Catalytic Mechanism of SiC-Based Catalyst Carriers

SiC can be used as a catalyst carrier not only because its excellent physical and chemical properties can meet all the requirements of a hard supporting material, but more importantly because SiC and the loaded active components have positive synergistic effects on the catalytic reaction process. When metallic active components and SiC form a metal–semiconductor catalytic system, the charge-transfer effect (Mott–Schottky effect) can effectively enhance the system’s catalytic performance [80,81,82]. When a metal is loaded on a semiconductor, Mott–Schottky contact occurs between the two components, and a metal–semiconductor heterostructure is formed at the interface. The heterojunction provides a basis for the charge-transfer effect between the metal and the semiconductor. It is similar to a pn junction and closely related to the respective work functions of the metal and the semiconductor.

The work functions of a metal and a semiconductor are expressed as follows:

W_m = E₀ − E_Fm

W_S = E₀ − E_Fs

where E₀ denotes the energy level in the vacuum, E_Fm denotes the metal’s Fermi energy level, and E_Fs denotes the semiconductor’s Fermi energy level. When a metal contacts an n-type semiconductor, if the metal’s work function (W_m) is greater than the work function of the semiconductor (W_S) the E_Fs of the semiconductor is higher than the E_Fm of the metal according to the above-mentioned formula. Therefore, when the two components are in contact, electrons will flow from the semiconductor with a higher system energy to the metal, thus equilibrating the Fermi energy levels of the two components and forming an electronic potential barrier on the semiconductor side [83]. SiC belongs to the n-type semiconductors [81]; therefore, the contact between a metal and SiC will result in the formation of a metal–semiconductor heterojunction as the metal active phase is dispersed on the SiC carrier. Such a heterojunction can cause the electrons of SiC to move rapidly toward the metal particles and form a metal active phase rich in electrons, which plays a very positive role in enhancing the catalytic performance [81,84,85,86,87,88,89,90,91,92,93,94,95].

It has been reported that the catalysts prepared via the synergistic effects between SiC and various metals had excellent catalytic performances. Generally, the metals used as active phases included Pd [85,86,90], Au [81,91,96], Pt [89,93], Ir [88], and Ni [92]. The active phases of a catalyst are of two types: single-metal and dual-metal active phases. The difference is that the dual-metal active phase takes advantage of the synergistic effects between two metals or between metals and the SiC carrier. For instance, Hao et al. [81] used Pd-Au dual-metal nanoparticles loaded on SiC to prepare a catalyst for the highly efficient photocatalytic hydrogenation of nitroaromatic hydrocarbons. Moreover, the electronic effect and the overall effect of Pd and Au could not only generate heterogeneous charged active sites, but also could enhance the photocatalytic activity of the catalyst for the hydrogenation of nitroaromatics by varying the electronic structure of the carrier’s surface [96,97,98,99].

In addition, metal–semiconductor (SiC) catalysts are mostly employed in photocatalytic reactions. Illumination can effectively amplify the oriented transfer of electrons. The photogenerated electrons can quickly transfer from SiC to metal particles, thus preventing the recombination of the photogenerated electrons and holes [88,92,100,101]. Jiao et al. [90] studied the Mott–Schottky heterojunction formed by Pd-SiC contact. The WF values of Pd and SiC were 5.12 eV and 4.0 eV, respectively, thereby forming a built-in potential of 1.12 eV. The formed potential forced the photogenerated electrons to transfer from the SiC carrier to Pd, which resulted in electron-rich Pd nanoparticles. The electron-rich Pd nanoparticles could activate iodobenzene and produce Pd-adsorbed aromatic groups. Additionally, the photogenerated holes on the SiC surface helped break the C–B bond [102] of phenylboronic acid and then further oxidized or reduced the activated materials to form the final products. In addition to photocatalytic reactions, metal–semiconductor (SiC) catalysts are also used in general catalytic preparation and conversion reactions for organic materials. Wang et al. [88] prepared γ-pentolactone (GVL) via the aqueous-phase hydrogenation of levulinic acid (LA) using an Ir/SiC catalyst and found that the catalyst exhibited high catalytic activity and stability in the reaction process. Similarly, there was Mott–Schottky contact between SiC and Ir; therefore, electrons transferred from the SiC carrier to Ir, which resulted in enhanced activity for hydrogenation.

In addition to the above-mentioned synergistic effects, there are other interactions between metals and the SiC carrier. Li et al. [95] used transition metals (Cu or Co) to modify a β-SiC carrier, which was then used to catalyze the hydrolysis of aminoborane to produce hydrogen. Cu and Co of the Cu-Co/β-SiC catalyst could modify the electronic properties of β-SiC and reduce the band gap of the semiconductor from 2.73 eV to 0.535 eV. The narrower band gap made the photocatalytic β-SiC carrier responsive to a wider UV–visible spectrum, thereby enhancing the catalytic performance. The metal active phase had the capability of varying the electronic properties and energy band structure of the SiC semiconductors; therefore, it was helpful in improving the intrinsic activity of SiC.

Due to the excellent physical and chemical properties of SiC-based catalyst carriers, they have gradually replaced the traditional catalyst carriers; moreover, the metal active phase dispersed on the surface of a SiC carrier exhibits synergistic effects with the carrier. The catalytic performance has been enhanced under the synergistic effect of the two components, which provides a basis for the exploration of new catalysts with the SiC carrier. However, according to previous research, most of the metals used as active phases were noble metals, and there were only few studies on the synergistic effect between general transition metals (Fe, Co, and Ni) and SiC carriers. Therefore, we believe that when using SiC as a hard supporting material, exploring the interaction between SiC and the active phase will be one of the developmental directions in this field in the future.

4. Application of SiC-Based Catalyst Carriers

Owing to its special structure, SiC has the advantages of high thermal conductivity, high chemical stability, and excellent mechanical strength and wear resistance; thus, it has broad prospects for use as a catalyst support or carrier. SiC carriers with a high specific surface area can fully disperse the active components of the supported catalyst, increase the number of reactive sites, and enhance the reaction efficiency; they can be applied to a (1) high-temperature catalytic reaction, (2) strong exothermic reaction, (3) reaction under harsh conditions, etc. [103]. At present, the research on SiC-based catalyst carriers is mainly focused on using their own advantages and employing different preparation methods to meet specific application conditions. The research not only simply pursues the preparation of SiC with a high specific surface area, but also seeks to meet practical application purposes. This mainly includes SiC surface modification, structure construction, and preparation of composite materials.

4.1. Surface Modification

The modification treatment for catalyst carriers can enhance the overall performance of the catalysts. The modification methods required for different catalytic reactions are also different, but all of them are used to meet practical production applications. Moreover, modified SiC as a catalyst carrier can increase the efficiency of the catalytic reaction, and it also plays a positive role in achieving production with low energy consumption and environmental protection.

Li et al. [104] explored the surface modification of SiC carriers and conducted related studies on the surface structure of SiC carriers tailored for the copper-catalyzed dehydrogenation of ethanol to acetaldehyde (DHEA). Currently, biomass-derived DHEA is a sustainable alternative to the processes based on fossil raw materials; for this method, copper is considered to be the most efficient catalyst. Meanwhile, they used SiC as a carrier and modified its surface to vary the interfacial properties from SiO₂-rich to C-rich; furthermore, they prepared a series of Cu-loaded catalysts (Cu/SiC, Cu/SiO₂/SiC, and Cu/C/SiC) to gain insights into the effects of the interfacial structure and composition on the DHEA process. They found that the SiO₂ surface facilitated the dispersion of copper NPs, thereby accelerating the conversion of ethanol. Furthermore, the carbon layer on the SiC substrate exhibited relatively inert characteristics that could inhibit the secondary reaction of the initially formed acetaldehyde by promoting the desorption of acetaldehyde from the carbon-rich surface; this enhanced the selectivity of the reaction. In other words, the surface modification of the carrier could significantly promote the DHEA process.

Noh et al. [105] used a calcium aluminate-modified, SiC-supported, nickel-based structural catalyst to refine methane vapor for the production of hydrogen. Steam reforming of methane (SRM) is an extremely important process for the production of hydrogen and synthesis gases (H₂ and CO). Common catalysts (Ni-based, alumina-supported catalysts) used in the SRM process suffer from the disadvantages of coke formation and sintering, which seriously affect the progress of the reaction. Alkali carriers such as calcium aluminate (CAx) show an excellent anti-carbon deposition capability, but to enhance their low thermal conductivity, nickel-based structural catalysts loaded on SiC-modified CAx have been prepared. The specific surface area of the synthesized carrier was larger (23–106 m²/g) and the overall performance of the catalyst was enhanced because the introduction of SiC increased the catalytic activity and coking resistance. In recent years, global resource crises and environmental problems have emerged one after another, and hydrogen has become an important clean energy source for the future. Efficient hydrogen production via the SRM process is of great significance for energy regeneration and ecological environmental protection at present and in the future.

Pathak et al. [106] studied the application of Fe₂O₃ NP catalysts supported by SiO₂-modified SiC for highly endothermic and corrosive decomposition reactions of sulfuric acid. For general catalyst carriers, due to poor thermal stability, active components (such as metal NPs) often agglomerate, aggregate, and sinter in a high-temperature and highly corrosive reaction environment. After fully analyzing the characteristics and advantages of SiC such as high thermal conductivity, high temperature resistance, and chemical inertness, they modified SiC with SiO₂ and dispersed Fe₂O₃ NPs on the SiO₂-modified SiC. This modification further varied the surface properties and the metal–support interaction on the interface, accordingly reducing the agglomeration at high temperatures and enhancing the stability. As a result, the decomposition reaction of sulfuric acid could proceed better. This was achieved mainly by forming an interface between the metal oxide NPs and support materials with enhanced heat transfer. The introduction of active metal–carrier interactions at the interface (Fe₂O₃-SiO₂-SiC) decreased the interaction between active phase–active phase (Fe₂O₃-Fe₂O₃), thereby reducing the agglomeration at high temperatures and maintaining the high activity and stability of the catalyst under harsh conditions. Pan et al. [107] applied a porous TiO₂ aerogel-modified SiC ceramic carrier in the integration of low-temperature denitration and dust removal, which realized the simultaneous removal of NO and dust from a low-temperature exhaust gas. The catalyst carrier was prepared by coating a TiO₂ sol on the surface of a SiC ceramic film carrier, which could be termed a nano-TiO₂ transition layer [108]. Furthermore, the supported MnOx catalyst exhibited a better low-temperature catalytic performance than pure MnOx (the carrier could improve the dispersion and surface acidity of MnOx [109]), and the obtained MnOx/TiO₂/SiC catalytic film with the TiO₂ aerogel as the transition layer showed an extremely high dust removal efficiency. The purification technology for low-temperature exhaust gases can provide new ideas for developing low-energy-consumption, high-efficiency treatments for exhaust gases.

4.2. Construction of Structures

To achieve practical applications, constructing special structures is an effective way to improve the catalytic performance.

Ledoux et al. [45,46] adopted the SMS method to prepare a SiC material that inherited the shape and structure of the raw material with a high specific surface area. They used the SiC material with the high specific surface area as the catalyst carrier and applied it in the direct oxidation of H₂S to S [37]. At a lower temperature (333 K), Ni was used as the main catalyst, and the TEM micrographs verified that Ni was well dispersed on the SiC surface. As shown in Figure 4, the hydrophilic layer of SiC was distributed in the pores, whereas the active phase NiS₂ was deposited therein. The water film in the pores acted as a “conveyor belt” and removed the sulfur produced in the reaction continuously via capillary condensation. Subsequently, the sulfur was removed from the pores and stored in the hydrophobic part of the SiC carrier, and the water film was immediately destroyed. The mechanism also enabled the catalyst’s high catalytic activity. In addition, the solid sulfur in the product was deposited on the carrier’s surface in a non-uniform manner but still allowed the reactants to contact the active sites. At the same time, under the same conditions, Al₂O₃, SiO₂, and activated carbon were used as the catalyst carriers for the desulfurization experiments. However, with the formation and deposition of sulfur, the active sites were completely blocked, and these catalysts were immediately deactivated. At a higher temperature (483 K), the catalyst with Fe₂O₃ as the active component and SiC as the carrier also exhibited high catalytic activity, and its selectivity (S) was as high as 95%. Compared with the performance of conventional catalysts, the performance of SiC-based catalysts prepared via this method was excellent; this was attributed to the remarkable dispersion of the active phase, which depended on the high specific surface area of the carrier. In addition, the interaction between the active phase and the carrier reached a balance that not only promoted the action and selectivity of the active phase but also maintained the mechanical strength of the catalyst itself. At the same time, because of the high thermal conductivity of SiC, the temperature of the entire catalyst surface was uniform, due to which the catalyst was more stable than conventional catalysts and could maintain a high catalytic performance.

In addition to the SMS method, the nanocasting method can also realize a high specific surface area and a porous structure by introducing a template. For instance, Li et al. [110] adopted molecular sieves; namely, SBA-15, KIT-6, and MCM-41, as hard templates to prepare ordered mesoporous SiC with different structures via the nanocasting method and introduced Ni onto the SiC substrate to prepare a mesoporous Ni/SiC catalyst for dry reforming of methane (DRM). The specific surface areas of SBA-15, KIT-6, and MCM-41 were 615 m²/g, 488 m²/g, and 912 m²/g, respectively. The ordered mesoporous SiC carriers corresponding to the above-mentioned three templates were SiC-SBA-15, SiC-KIT-6, and SiC-MCM-41 with specific surface areas of 405 m²/g, 344 m²/g, and 96 m²/g, respectively. The first two SiC carriers prepared by using the SBA-15 and KIT-6 molecular sieves exhibited high specific surface areas; that is, SBA-15 and KIT-6 as mesoporous templates could be successfully replicated, which enabled the carriers to support active Ni better. As a transition metal, Ni is often used as the active component of catalysts due to its high catalytic activity and low cost [111,112]. However, in the DRM reaction, Ni often suffers from the disadvantages of carbon deposition and metal sintering, which result in rapid deactivation of the catalyst and thus limit the industrial application of Ni-based catalysts [113,114]. The confinement structure of ordered mesoporous/microporous materials can effectively suppress metal aggregation and carbon deposition, thereby further inhibiting the rapid deactivation of the catalysts [115,116,117,118]. Furthermore, the ordered mesoporous materials have high specific surface areas, regular pore arrays, and adjustable pore diameters, due to which they can be used as excellent carriers for catalytic reactions [119]. In summary, the construction of SiC carriers with a special structure to support active components can meet practical application requirements and significantly enhance the catalytic effect and reaction efficiency.

Jiang et al. [120] applied a SiC foam-based structured catalyst to the process for the oxidative dehydrogenation of 1-butene to butadiene. The SiC foam loaded with the ZnFe₂O₄-α-Fe₂O₃ (ZnFe₂O₄-α-Fe₂O₃/SiC) structural catalyst was prepared via the slurry-coating method. The conversion rate of the structural catalyst was considerably higher than that of the particle catalyst, which could effectively resolve the problems encountered in a conventional reactor such as a rapid adiabatic temperature rise and a large pressure drop, a low gas velocity and conversion rate, and high water consumption. Butadiene is the main raw material for manufacturing rubber, synthetic fibers, nylon intermediates, plastics, film-forming additives for fuels and oils, and other valuable products [121,122,123]. Moreover, with the development of petrochemical and coal chemical industries in China, the butene output continues to increase, whereas the output of butadiene is relatively lacking; the conversion of butene into butadiene can meet the market demand.

4.3. Preparation of Composite Materials

Dong et al. [29] proposed to develop composite materials for electrocatalysis. The introduction of EG on SiC can not only maintain the excellent properties of SiC but also increase the material’s electrical conductivity. The prepared Pt/SiC/EG catalyst exhibited a large electrochemically active surface area (97.4 m²/g). They prepared SiC/EG nanocomposites by carbothermic reduction as a high-performance catalyst for the oxidation reactions of methanol and ethanol. SiC/EG was the catalyst carrier that loaded active NPs to form the catalyst. Compared with the commercial Pt/C catalysts, the Pt/SiC/EG catalysts exhibited a larger electrochemically active surface area, higher electrocatalytic activity and durability, and a better tolerance to catalyst poisoning in the oxidation reactions of methanol and ethanol. The active Pt NPs were uniformly deposited on the SiC/EG carrier via the electrodeposition method, which resulted in extremely high dispersity. The Pt NPs in the Pt/SiC/EG catalyst were small in size and uniformly distributed on the SiC support; therefore, the Pt/SiC/EG catalyst exhibited a large electrochemically active surface area. Meanwhile, the SiC/EG support used to load NPs demonstrated a high corrosion resistance and a porous network structure; therefore, the Pt/SiC/EG catalyst exhibited an excellent electrocatalytic performance. In SiC-coated graphite nanocomposites, the graphite core endows the material with high electrical conductivity and high chemical stability; on the other hand, as a coating shell, SiC can not only prevent the reaction between graphite and oxygen but also enhance the wear resistance. Dong et al. [124] prepared a Pt/B0.1SiC catalyst via the cyclic voltammetric deposition of Pt NPs using boron-doped SiC (B0.1SiC) synthesized through carbothermic reduction as a carrier. The electrochemically active surface areas of Pt/SiC and Pt/B0.1SiC were 87.9 and 95.1 m²/g, respectively, which indicated that there were more electrochemically active sites on the Pt/B0.1SiC. According to previously reported studies, the doping of boron can effectively increase the conductivity of SiC. The low doping content of boron increases the concentration of charge carriers in SiC. The increase in boron content even endows SiC with superconductivity [125]. In the electro-oxidation of methanol, the catalyst exhibited higher catalytic activity. The catalytic activity and chemical stability of Pt/B0.1SiC (prepared via the surface electrodeposition of B0.1SiC synthesized through carbothermal reduction) in the electro-oxidation of methanol were higher than those of Pt/SiC prepared via the same method because doping B atoms into the lattice sites of SiC led to increased carrier concentration and an enhanced charge-transfer ability. In addition, the Pt NPs loaded on B0.1SiC demonstrated higher dispersity and a smaller particle size than the Pt NPs loaded on SiC; therefore, the catalyst exhibited a larger electrochemically active surface area.

Zhang et al. [126] developed a mono-plate SiC foam-supported Ni-La₂O₃ composite catalyst that showed high activity and stability in the DRM process, which used methane and carbon dioxide. The integrated SiC foam with high thermal conductivity ensured uniform heat distribution and prevented the formation of “cold spots” in the catalyst bed (in intense endothermic DRM reactions, the “cold spots” formed in the catalyst bed are detrimental to the catalyst performance [127]; the reason is that the “cold spots” lead to severe carbon deposition and deactivation of the catalyst [128]). La₂O₃ could eliminate the intermediate species in carbon deposition, enhance the activity of the catalyst, and prolong the life of the catalyst. Moreover, the “Ni-La₂O₃” nanocomposite ensured complete contact between Ni and La₂O₃, which resulted in strong Ni-La₂O₃ interactions to prevent the Ni from sintering. The DRM process can solve not only the problem of carbon dioxide emissions but also the issue of the low utilization of energy sources such as biogas.

Wang et al. [129] utilized a NiMgAl/SiC composite catalyst derived from a hydrotalcite precursor on a SiC substrate for the methanation of CO₂. The composite catalyst showed high low-temperature activity and excellent long-term stability. Compared with NiMgAl and Ni/SiC catalysts, the higher specific surface area of the NiMgAl/SiC composite catalyst led to the formation of smaller Ni NPs on the carrier, which was beneficial to obtaining high activity in the methanation of CO₂. The NiMgAl/SiC composite catalyst with a hydrotalcite-like structure combined with the SiC matrix was synthesized via a co-precipitation method in which the high thermal conductivity and excellent thermal stability of SiC were fully utilized. Due to the excellent properties together with the small and highly reducible Ni NPs supported, the catalyst exhibited a higher stability and higher catalytic activity. Furthermore, methanation of CO₂ is an important reaction in the field of energy and environment, and it is also one of the important strategies in energy regeneration. More importantly, the development of renewable energy has far-reaching significance in low-carbon environmental protection, ecological governance, and energy progress.

Through the above-mentioned three application methods for SiC carriers, the catalysts in various production processes and reactions are better supported, and the overall catalytic activity and efficiency are considerably enhanced. However, in practical applications, there are a few SiC-based catalyst carriers that are synthesized from waste materials and at lower temperatures. Resource reuse and synthesis with low energy consumption are the developmental trends of industrial production. Therefore, SiC with a high surface area prepared at low temperatures using waste as the raw material (or a raw material precursor) should be used as a catalyst carrier. Moreover, modification and construction of special structures and the application of composite materials containing SiC to actual industrial production are the future developmental directions of this field.

5. Conclusions and Prospects

Compared with conventional catalyst carriers, SiC-based catalyst carriers have broad application prospects due to their outstanding thermal conductivity, excellent mechanical strength and wear resistance, and remarkable chemical stability. In recent years, many experts and researchers have mainly focused on increasing the specific surface area of SiC carriers to enhance their performance because a large surface area can better disperse the active components and increase the number of reactive sites. However, the specific surface area of conventional SiC materials is small. Therefore, research on increasing the specific surface area is the key step to further improve the performance of SiC carriers on the original basis. The specific methods were as follows: SiC nanomaterials were prepared via the sol-gel method and carbothermic reduction; the shape memory synthesis method was used to maintain the characteristics of high specific surface areas of the raw materials; and structural SiC materials were obtained via the nanocasting method. In terms of application, the previous preparation methods were modified to meet special application requirements mainly through the construction of a SiC surface, modification and construction of special structures, and preparation of composite materials. We believe that the main purposes of using SiC as a catalyst carrier are to inherit the original advantageous characteristics of SiC through various technical means and also to obtain other special properties to meet various production needs. With the development and application of heterogeneous catalysts, the numerous drawbacks of traditional catalyst carriers have been exposed, due to which they are not suitable for some special industrial production; on the other hand, SiC-based catalyst carriers have gradually emerged due to their advantages. Although there have been a few commercial cases of the use of SiC as a catalyst carrier, many researchers were concerned with its practical application in various areas, and their research results indicated its huge development potential.

However, the preparation methods for SiC carriers generally have disadvantages such as the requirements for high temperatures and energy consumption. Therefore, we had several views on the development of SiC-based catalyst carriers:

(1)

The preparation of SiC-based catalyst carriers using waste as the raw material not only saves costs but also conforms to the concept of reutilization of resources and ecological environmental protection. However, the specific surface area of SiC prepared by using waste is relatively low, due to which it can meet the requirements of a catalyst carrier only to a certain extent, and the overall performance of the catalyst is still limited. Therefore, the use of waste to prepare SiC-based catalyst carriers with a high specific surface area has very broad prospects, and therefore is one of the developmental directions of this field in the future.

(2)

The preparation of SiC-based catalyst carriers at low temperatures can also greatly reduce the production cost. The preparation temperatures of SiC are generally high. If SiC-based catalyst carriers can be prepared at low temperatures by improving and innovating the present technical means, their commercial value can be directly increased with a more extensive range of applications.

(3)

In the construction of porous SiC nanostructures and the use of waste to prepare SiC-based catalyst carriers at low temperatures in combination with the first two innovations, it was found that the specific surface area of SiC nanomaterials with a porous structure was large, and the performance of the catalyst loaded on such carriers was considerably enhanced.

(4)

The synergistic effect of SiC with its supported metal active phase needs to be further explored.

We believe that with the gradual improvement in SiC-based catalyst carriers, the low-temperature preparation of porous SiC carriers using waste materials as raw materials can become the developmental direction and trend in this field.