Search Results (7)

The main goal of this work was to determine the role of copper in bimetallic nickel–copper BEA zeolite catalysts prepared by sequential impregnation and co-impregnation, as well as defining the influence of the method of impregnation on the catalytic activity of the described catalysts. The all-prepared samples were tested in hydrocracking reactions with rapeseed oil as a feedstock. The physicochemical properties of the catalytic materials were determined using H₂-TPR, TPD-NH₃, XRD, BET, and SEM-EDS techniques. The reaction products were analyzed using chromatographic techniques (HPLC and GC-MS). The bimetallic systems obtained post-impregnation exhibited lower conversions of rapeseed oil than catalysts synthesized by co-impregnation. For all bimetallic catalysts, oil conversion was higher than for the monometallic copper BEA zeolite catalyst. This indicates that nickel is responsible for better oil conversion. The highest oil conversion (92.7%) was noted for the co-impregnated 5%Ni-5%Cu_BEA zeolite catalyst. For all tested catalysts, the highest selectivity was noted for the gasoil fraction. However, the presence of copper in bimetallic Cu-Ni_BEA zeolite catalysts led to increased selectivity towards gasoline and kerosene compared to the monometallic nickel BEA zeolite catalyst. Full article

In our previous work, we fabricated Ni single-atoms within Beta zeolite (Ni₁@Beta-NO₃⁻) using NiNO₃·6H₂O as a metal precursor without any chelating agents, which exhibited exceptional performance in the selective hydrogenation of furfural. Owing to the confinement effect, the as-encapsulated nickel species appears in the form of Ni⁰ and Ni^δ+, which implies its feasibility in metal catalysis and coordination catalysis. In the study reported herein, we further explored the hydrogen production and olefin oligomerization performance of Ni₁@Beta-NO₃⁻. It was found that Ni₁@Beta-NO₃⁻ demonstrated a high H₂ generation turnover frequency (TOF) and low activation energy (E_a) in a sodium borohydride (NaBH₄) hydrolysis reaction, with values of 331 min⁻¹ and 30.1 kJ/mol, respectively. In ethylene dimerization, it exhibited a high butylene selectivity of 99.4% and a TOF as high as 5804 h⁻¹. In propylene oligomerization, Ni₁@Beta-NO₃⁻ demonstrated high selectivity (75.21%) of long-chain olefins (≥C₆⁺), overcoming the problem of cracking reactions that occur during oligomerization using H-Beta. Additionally, as a comparison, the influence of the metal precursor (NiCl₂) on the performance of the encapsulated Ni catalyst was also examined. This research expands the application scenarios of non-noble metal single-atom catalysts and provides significant assistance and potential for the production of H₂ from hydrogen storage materials and the production of valuable chemicals. Full article

Coal fly ash and acid mine drainage are significant environmental issues in South Africa, causing storage constraints and impacting water quality. This study explores the use of coal fly ash and acid mine drainage in preparing zeolite HBEA-supported Fe catalysts. The Na-BEA parent catalysts were synthesised hydrothermally using coal fly ash as a feedstock. The Fe was loaded upon the H-BEA form zeolite using liquid-phase ion exchange or wet impregnation, using Fe-rich acid mine drainage as the metal precursor. The ion-exchanged Fe-BEA catalysts exhibited excellent activity, with the highest selectivity achieved over the 25 AHW after 0.5 h on stream. The study also found that when impregnation was used to load Fe onto the zeolite support, other metals present in the AMD affected the overall activity, with Mn, Ca, Mg, and Na decreasing conversion and selectivity, while Ni had a promoting effect. This study demonstrates that green solid acid catalysts with high catalytic activity can be prepared using two waste materials, coal fly ash and acid mine drainage. To the best of our knowledge, we are reporting for the first time the use of acid mine drainage as a metal precursor in Fe-BEA catalyst preparation. Full article

Lignin is one of the main structural components of lignocellulosic biomass and can be utilized to produce phenolic compounds that can be converted downstream to cycloalkanes and aromatics, which are useful as drop-in road or aviation biofuels. Within this study, the hydrodeoxygenation of model phenolic/aromatic compounds and surrogate mixture simulating the light fraction of lignin fast-pyrolysis bio-oil was performed under mild reaction conditions. Ni/BEA zeolite was selected as a catalyst to investigate the conversion and the product selectivity of alkyl phenols (phenol, catechol, cresols), methoxy-phenols (guaiacol, syringol, creosol), aromatics (anisole, 1,2,3-trimethoxybenzene) and dimer (2-phenoxy-1-phenyl ethanol) compounds towards (alkyl)cycloalkanes. The hydrodeoxygenation of a surrogate mixture of eleven phenolic and aromatic compounds was then studied by investigating the effect of reaction conditions (temperature, time, H₂ pressure, surrogate mixture concentration, and catalyst-to-feed ratio). The conversion of model compounds was in the range of 80–100%, towards a 37–81% (alkyl)cycloalkane yield, being strongly dependent on the complexity/side-chain group of the phenolic/aromatic ring. Regarding the hydrodeoxygenation of the surrogate mixture, 59–100% conversion was achieved, with up to a 72% yield of C₆–C₉ cycloalkanes. Characterization of spent catalysts showed that the hydrodeoxygenation of surrogate mixture led to carbonaceous depositions on the catalyst, which can be limited under lower temperatures and longer reaction conditions, while after regeneration, the physicochemical properties of catalysts can be partially recovered. Full article

The aim of this work was to investigate the hydrocracking of algae oil derived from Spirulina Platensis species catalyzed with bi-component nickel-zirconia catalysts supported onto different carriers (BEA, ZSM-5 and Al₂O₃) in an autoclave at 320 °C for 2 h with a hydrogen pressure of 75 bar. All catalysts were prepared using the wet co-impregnation method and were characterized by H₂-TPR, XRD, NH₃-TPD, BET and SEM-EDS. Before reactions, catalysts were calcined at 600 °C for 4 h in a muffle furnace, then reduced with 5%H₂-95%Ar reducing mixture at 500 °C, 600 °C or 700 °C for 2 h. The obtained products were analyzed and identified by HPLC and GC-MS techniques. In addition to the investigation of the support effect, the influence of the reduction temperature of catalytic systems on the catalytic activity and selectivity of the products was also examined. The activity results show that Ni-Zr systems supported on zeolites exhibited high conversion of algal oil. A gradual decrease in conversion was observed when increasing the reduction temperature of the catalyst (from 500 °C to 600 °C and 700 °C) for BEA zeolite catalysts. The reaction products contain hydrocarbons from C₇ to C₃₃ (for zeolite-supported catalysts) and C₃₆ (for systems on Al₂O₃). The identified hydrocarbons mainly belong to the gasoil fraction (C₁₄–C₂₂). In the research, the best catalyst for the algal oil hydrocracking reaction was found to be the 5%Ni-5%Zr/BEA system reduced at 600 °C, which exhibited the second highest algal oil conversion (94.0%). The differences in catalytic activity that occur are due to the differences in the specific surface area among the supports and to differences in the acidity of the catalyst surface depending on the reduction temperature. Full article

As the utilization of zeolites has become more frequent in the dry reforming of methane (DRM) reaction, more systematic studies are required to evaluate properly the influence of zeolites’ composition and framework type on the performance. Therefore, in this work, a step-by-step study was performed with the aim of analyzing the effects of Ni loading (5, 10 or 15 wt.% over USY(3) zeolite), Si/Al ratio (3, 15 or 38 on USY zeolites with 15 wt.% Ni) and framework type (USY, BEA, ZSM-5 or MOR for 15 wt.% Ni and Si/Al ratios of ≈40) on catalysts’ properties and performances. Increasing Ni loadings enhanced CH₄ and CO₂ conversions even though the catalysts’ stability was decreasing over the time. The variation of the Si/Al ratio on USY and the use of different zeolites had also a remarkable impact on the catalytic performance. For instance, at 500–600 °C reaction temperatures, the catalysts with higher basicity and reducibility exhibited the best results. However, when the temperature was further increased, catalysts presenting stronger metal–support interactions (nickel nanoparticles located in mesoporous cavities) displayed the highest conversions and stability over time. In brief, the use of 15 wt.% Ni and a USY zeolite, with both micro- and mesopores and high surface area, led to the best performances, mainly attributed to a favorable number of Ni⁰ active sites and the establishment of stronger metal–support interactions (due to nanoparticles confinement inside the mesopores). Full article

Specific features of the catalytic tar cracking in the presence of formic acid, BEA zeolite and 8% Ni-2.5% Mo/Sibunit catalyst were studied at 350 °C and 1.0 MPa pressure. The obtained results evidenced that formic acid can be used as a hydrogen donor during catalytic reactions. The formic acid addition made it possible to perform efficient hydrocracking of heavy feed such as tar. It was found that both the tar conversion and selectivity to light (gasoline-diesel) fractions grew in the sequence: tar < (tar - formic acid) < (tar - formic acid - BEA zeolite) < (tar - formic acid - BEA zeolite - 8% Ni-2.5% Mo/Sibunit catalyst). Furthermore, significantly lower concentrations of impurities containing sulfur and nitrogen were observed for the (tar - formic acid - BEA zeolite - 8% Ni-2.5% Mo/Sibunit catalyst) system. For example, the sulfur and nitrogen concentrations in the tar precursor were 1.50% and 0.86%, respectively. Meanwhile, their concentrations in the liquid products after the catalytic cracking were 0.73% and 0.18%, respectively. Full article