# Prospects and Technical Challenges in Hydrogen Production through Dry Reforming of Methane
## 2 Recent Advances on Catalysts for Syngas Production
### Noble Metal-Based Catalysts  
The catalytic activity of noble metals from groups VIII to X (Ru, Rh, Ir, Pd, Pt) has been thoroughly investigated towards DRM when supported over different materials. These noble metals present high catalytic activity for CH\({}_{4}\) and CO\({}_{2}\) conversion (X\({}_{\text{CH}_{4}}\) and X\({}_{\text{CO}_{2}}\), respectively) and distinct stability against thermal and oxidative sintering and, especially, coke deposition [14; 15]. The observed activity of noble metals for DRM follow the order Rh > Ru > Ir > Pt > Pd [16]. Nonetheless, the use of noble metals for such purpose still present, as major drawbacks, the low abundance, high costs and usual toxicity [17]. Recently, research has focused not only on highly active catalysts using noble metals at low concentrations (Table 1), which has been proven effective, but also on the promoting effects of noble metals for transition metal-based catalysts, aiming to enhance their resistance against coke deposition [18; 19]. Ruthenium is one of the cheapest noble metals (still almost 500 times more expensive than nickel) that presents a good catalytic performance for DRM [16]. [PERSON] et al. [20] explored the effect of different supports (Al\({}_{2}\)O\({}_{3}\), MgAl\({}_{2}\)O\({}_{4}\) and YSZ) on the DRM activity of mono- (Ru) and bimetallic (Ru, Ni) catalysts for hydrogen production. Despite the high catalyst activity of monometallic Ru/Al\({}_{2}\)O\({}_{3}\) catalyst (T = 750 \({}^{\circ}\)C, X\({}_{\text{CH}_{4}}\) = 90%, X\({}_{\text{CO}_{2}}\) = 93%, H\({}_{2}\)/CO = 0.94), the highest hydrogen production was obtained when 5 wt% Ni/Al\({}_{2}\)O\({}_{3}\) catalyst was promoted with 1 wt% Ru (T = 750 \({}^{\circ}\)C, X\({}_{\text{CH}_{4}}\) = 94%, X\({}_{\text{CO}_{2}}\) = 97%, H\({}_{2}\)/CO = 0.97). Ru functionalization also increased the overall catalyst stability by preventing catalyst sintering and the formation of poorly active phases, such as NiAl\({}_{2}\)O\({}_{4}\) for the Ru-Ni/Al\({}_{2}\)O\({}_{3}\) catalyst. On the other hand, poor metal dispersion after Ru promotion (maximum dispersion of 6%) was responsible for an increase in carbon deposition over the Ni-based catalyst (from 0.18% to 0.32% for Ni/Al\({}_{2}\)O\({}_{3}\) and Ru-Ni/Al\({}_{2}\)O\({}_{3}\), respectively) [20]. A high metal dispersion was found to promote a stronger interaction between Ru particles and the catalyst support and lead to lower carbon deposition and increased catalyst stability [21]. [PERSON] et al. [22] investigated the performance of partially substituted perovskites LaAlO\({}_{3}\) by 2 wt% of noble metals Ru, Pt and Pd for the DRM reaction at 800 \({}^{\circ}\)C. The authors reported that Ru-substituted LaAlO\({}_{9.88}\)Ru\({}_{0.02}\)O\({}_{3-8}\) presented the highest hydrogen production, reaching a H\({}_{2}\)/CO ratio 0.85 with CH\({}_{4}\) and CO\({}_{2}\) conversions of 86% and 100%, respectively. Strong occurrence of RWGS reaction along with DRM was responsible for straying the H\({}_{2}\)/CO from unity in all cases, especially on the Pt-substituted  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Catalyst** & **Preparation** & **Reaction Conditions** & **X\({}_{\text{CH}_{4}}\)(\%)** & **X\({}_{\text{CO}_{2}}\)(\%)** & **H\({}_{2}\)/CO** & **Coke** & **Ref.