# Prospects and Technical Challenges in Hydrogen Production through Dry Reforming of Methane
## 2 Recent Advances on Catalysts for Syngas Production
### Transition Metals-Based Catalysts
#### 2.2.5 Role of Catalyst Support  
Although studies have stated that the catalyst support itself would not take part in the DRM reaction [16], it has been demonstrated that several support's features, such as the surface basicity, oxygen mobility and storage capacity, as well as the ability of interacting with active phases, influence catalytic performance [64; 90]. The support's surface acidic-basic equilibrium may influence the reaction performance in several different aspects. While acidic sites favor CH\({}_{4}\) cracking, which leads to carbon formation [96], the increase in the support's basicity is related to an enhanced removal of carbon deposits, which may lead to higher catalyst stability [97]. [PERSON] et al. [98] indicate that such acidic-basic equilibrium on the catalyst support may also influence the electronic environment of the active sites and further favor/inhibit side reactions such as CH\({}_{4}\) cracking and CO disproportionation. The addition of MgO to Al\({}_{2}\)O\({}_{3}\) support is a well-described method of increasing support basicity for DRM. [PERSON] et al. [99] have described the role of MgO as two-fold. First, the basic properties of MgO increase the adsorption of CO\({}_{2}\), which leads to a higher release of oxygen on the support's surface and, in turn, increases the coke resistance via the gasification of carbon deposits (reverse Boudouard reaction). Second, the presence of MgO leads to the formation of a layered double hydroxide, in which the Mg\({}^{2+}\) and Al\({}^{3+}\) ions are uniformly dispersed and help decrease the agglomeration of active metal particles and, in turn, increase sintering resistance. On the other hand, excessive basicity may also lead to carbon deposition, decrease metal dispersion, lead to lower H\({}_{2}\)/CO ratios and compromise the overall catalyst performance [98; 100]. [PERSON] et al. [97] investigated the optimization of the MgO content on Al2O3-supported Ni catalysts for DRM and reported that the highest H\({}_{2}\)/CO = 0.95 (T = 800 \({}^{\circ}\)C, \(\chi_{\text{CH}_{4}}\) = 86%, \(\chi_{\text{CO}_{2}}\) = 91%) was obtained with 2.0 wt% MgO, while higher contents were actually detrimental for the process. [PERSON] et al. [101] evaluated hydrogen production over a series of transition metall-modified (Ti, Mo, Si, W) alumina supports with Ni active phase and reported that adding Si and W increased catalyst thermal stability and yielded 60% and 70% H\({}_{2}\) production, respectively, at T = 700 \({}^{\circ}\)C. In this study, the authors highlighted the importance of metal-support interaction on the catalyst activity and showed that harmful interactions between the active phase and the oxide support may significantly compromise the catalyst performance. The formation of poorly active NiTiO\({}_{3}\) and NiMoO species, for example, on Ti- and Mo-modified alumina was responsible for a drop in H\({}_{2}\) yields to 30% and 45%, respectively, at T = 700 \({}^{\circ}\)C.  
Ceria and ceria-modified supports have been investigated for their oxygen storage abilities due to the capacity of cerium to easily change oxidation states from Ce\({}^{4+}\) to Ce\({}^{3+}\). Studies have shown that high oxygen retention accounts for a higher catalyst reducibility, which may lead to increased activity, as well as higher oxygen mobility and carbon gasification effectiveness [102; 103]. The oxygen mobility on the catalyst support bulk structure may influence not only the reaction mechanisms, for example, under DRM conditions, but also the metal-support interaction and the overall catalyst stability [104]. On DRM process, the role of oxygen vacancies on the reaction mechanism is two-fold. First, the oxygen vacancies in the lattice of the support act as activation sites for the CO\({}_{2}\) to promote the cleavage of the C-O bonds, which increases the overall amount of oxygen in the support surface.