**4.3 Catalysts for dry reforming approach**

Numerous studies on the development of active and coking-resistant DRM reaction catalysts have been published [102, 103]. Common DRM catalysts are backed by noble metal catalysts like Ru, Rh and Pt and backed by transition metal catalysts like Ni and Co [104–106]. The calculations for the result showed that noble Ru and Rh metals exhibit greater activity than Ni as long as the particle sizes and dispersion are the same [106]. While noble metals such as Ru, Rh and Pt in the DRM response are very effective and more resistant to coking than other transition metals, they are not readily accessible and are also costly [104].

#### *4.3.1 Nickel based catalyst material*

Ni-based catalysts are the most frequently used for commercial purposes on an industrial scale. In order to commercialize the industrial sector DRM response, the primary focus is on developing inexpensive and cost-effective catalysts with high activity and high carbon deposition resistance. Researchers performed research on the sort of assistance used and the impacts of adding promoters to Ni-based catalysts in order to define the most efficient way to enhance their coking resistance. In addition, latest efforts to enhance catalytic activity and inhibit carbon formation are aimed at combining two or three metals as active locations [105, 107]. Pretreatment process preparation method and catalyst also play a crucial role in altering structural characteristics, implementing behavior decrease and enhancing catalytic efficiency [108]. Besides establishing the Ni-based catalyst with certain modifying agents in the catalyst preparation, the incorporation of Ni particles in the mesoporous aid could also enhance the conversion of reactants and the yield of products by preventing the sintering of metal particles and improving the metalsupporting connection. This metal produces desirable results due to the high specific region of mesoporous materials which can increase the dispersion of Ni particles on the supported catalyst [109].

In addition, the strong interaction between metal and support stabilizes the Ni particles incorporated in the mesoporous matrix. Multiple contact regions between the Ni particles and the support could improve thermal stability and support metal cooperation and support. The incorporation of Ni-based catalysts into mesoporous supports such as MCM-41, SBA-16, TUD-1, meso-Al2O3 and meso-ZrO2 has, as reported in the literature, demonstrated high catalytic activity and high carbon resistance in DRM. Catalyst supports can also be synthesized from plants, which is crucial for the effectiveness of DRM catalysts. The use of polymers from trees has been an interesting region among scientists in latest years with the aim of increasing the velocity of chemical reactions. In addition to generating high-quality chemicals, catalysts installed on commonly accessible cellulose incur low manufacturing expenses [110].

Abimanyu et al. [111] reported that the main steps to synthesize catalyst supports are pretreatment and hydrolysis. Ni-based catalysts have been used industrially as metal precursors in DRM, but the need to refine the metal to improve catalyst performance has recently attracted the interest of many scientists, as these particles demonstrated promising physical and chemical properties with elevated technological applications potential.

The preparation technique significantly affected a catalyst's physico-chemical characteristics and efficiency, according to Jang et al. [112]. It has therefore been noted that impregnation and co-precipitation are the most commonly used standard techniques of catalyst preparing. Another less prevalent technique for preparing catalysts is sol-gel, which generates a distribution of fine size. This method reduces the deactivation rate, offers high thermal resistance to agglomeration and creates a product of high quality compared to conventional methods.

A new non-thermal glow discharge plasma method has recently been developed to improve metal support interaction, boost the distribution of Ni particles and improve the activity and stability of the catalyst [113]. However, in comparison with simpler preparation techniques, plasma therapy is comparatively costly. This would improve the activity and stability of the catalyst in the DRM response by combining novel catalytic material and techniques.

Supported bimetallic catalysts demonstrate increased DRM activity and stability based on Zhang et al. [114] study. The preparation technique is one of the main variables responsible for the bimetallic catalyst's outstanding catalytic results. During catalyst preparing, the use of high calcining temperature outcomes in strong interactions between metal and support, which converts the catalyst into stable frame-like constructions. In particular, carbon formation is efficiently blocked during the catalyst decrease by using Ni-Co alloy compared to using single Ni sites. The synthesis method of different catalysts also affects the reaction effectiveness. For example, the method of co-precipitation may produce smaller sizes of metal particles compared to the use of wet impregnation.
