**1. Introduction**

Carbon dioxide (CO2) and methane (CH4) contribute to the increasing of the Earth's temperature. A reaction that can reduce the concentration of these gases is the dry reforming of methane, DRM (Equation (1)); this reaction can be very beneficial for the environment.

$$\text{CH}\_4 + \text{CO}\_2 \rightarrow 2\text{CO} + 2\text{H}\_2, \Delta \text{H}^\circ = 247.3 \text{ kJ mol}^{-1} \tag{1}$$

In addition to the possible use of DRM for mitigating greenhouse gases involved in global warming, it can generate sustainable hydrogen and syngas (CO + H2). Syngas can be used as fuel and to produce a wide range of chemicals including methanol and hydrocarbons to make synthetic fuel [1]. DRM is of scientific and commercial importance [2,3].

Noble metal and base metal catalysts have been proposed for DRM [1]. Nickelbased metal catalysts have the potential to compete with noble metal-based catalysts when comparing their catalytic performance, cost, and abundance of the raw materials [2]. However, the existence of side reactions such as carbon monoxide disproportionation and methane decomposition brings challenge of coping with the deactivation of Ni catalysis due to coke deposits [2–4]. These are more problematic in DRM than in processes that include steam [4]. Moreover, sintering of metal particles also plays a role in decreasing the catalytic activity due to reducing the exposed active metal surface area. The improvement

**Citation:** Khan, W.U.; Khan, M.R.; Busquets, R.; Ahmad, N. Contribution of Oxide Supports in Nickel-Based Catalytic Elimination of Greenhouse Gases and Generation of Syngas. *Energies* **2021**, *14*, 7324. https://doi.org/10.3390/en14217324

Academic Editor: João Fernando Pereira Gomes

Received: 6 October 2021 Accepted: 1 November 2021 Published: 4 November 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

in catalytic activity performance and resistance to carbon deposition in Ni catalysis can be achieved by employing various preparation strategies leading to favorable structures (for instance, by adding promoters [5–9], selecting a suitable support which is usually a metal oxide [10–13], optimizing metal loading or using bimetallic active sites [3]). Among these strategies to reduce carbonaceous deactivation of the catalyst, catalyst supports offer advantages such as the possibility of dispersing metal catalyst nanoparticles over their surface. This enhances resistance to carbon deposition and can improve their catalytic activity [14]. The 3D network in zeolite supports, formed by shared oxygen atoms of SiO4 and AlO4 tetrahedra, possess high resistance to temperature and mechanical stability due to their ordered framework. Moreover, zeolites offer crystalline features such as uniform microporosity (diameter < 2 nm), and pore shape that gives selectivity by controlling the entrance and exit of reactant molecules in zeolite channels [15–18]. The unique shape selectivity feature of zeolites lies behind their application as catalysts and adsorbents in various industries [19,20]. Moreover, suitable properties of zeolites including their high specific surface areas, well-defined microporous structure, high thermal stability and high capacity of CO2 adsorption [21,22] can play a role in catalysis. In addition, their potential in offering high metal dispersion, superior resistance to carbon formation, and suitable metal-support interaction has also attracted scientists towards utilizing zeolites as catalyst supports in the DRM reaction. Ni based catalysts supported on different zeolites have been reported for DRM reaction [23–29]. Hambali et al. [29] synthesized mesoporous fibrous MFI support via the microemulsion method and deposited Ni over support surfaces using double solvent, wetness impregnation, and physical mixing methods. The catalytic activity results revealed that Ni based catalysts prepared by wetness impregnation exhibited stable performance with least carbon deposition as compared with catalysts synthesized by double solvent or physical mixing approaches. It was found that the acidity of the support hindered the side reaction i.e., methane cracking mainly responsible for carbon deposition at high reaction temperatures (800 ◦C).

Keeping in mind the distinct properties of zeolites, this work fills the literature gap by providing an insight into the role of reducibility, carbon dioxide adsorption capacity, and basicity of zeolites in displaying stable performance during DRM. Furthermore, the aim of this research is to identify a conventional support that can enhance DRM, determine how zeolite supports can affect the DRM reaction, and determine how their stability and performance compares with conventional alumina supported Ni catalysts.

### **2. Materials and Methods**
