Insights into the Mechanism of Methanol Steam Reforming for Hydrogen Production over Ni–Cu-Based Catalysts

Density Functional Theory Study of Methanol Steam Reforming on Pt3Sn(111) and the Promotion Effect of a Surface Hydroxy Group

Methanol steam reforming (MSR) is studied on a Pt3Sn surface using the density functional theory (DFT). An MSR network is mapped out, including several reaction pathways. The main pathway proposed is CH3OH + OH → CH3O → CH2O → CH2O + OH → CH2OOH → CHOOH → COOH → COOH + OH → CO2 + H2O. The adsorption strengths of CH3OH, CH2O, CHOOH, H2O and CO2 are relatively weak, while other intermediates are strongly adsorbed on Pt3Sn(111). H2O decomposition to OH is the rate-determining step on Pt3Sn(111). The promotion effect of the OH group is remarkable on the conversions of CH3OH, CH2O and trans-COOH. In particular, the activation barriers of the O-H bond cleavage (e.g., CH3OH → CH3O and trans-COOH → CO2) decrease substantially by ~1 eV because of the involvement of OH. Compared with the case of MSR on Pt(111), the generation of OH from H2O decomposition is more competitive on Pt3Sn(111), and the presence of abundant OH facilitates the combination of CO with OH to generate COOH, which accounts for the improved CO tolerance of the PtSn alloy over pure Pt.

Effect of Fe-loading in iron-based catalysts for the CH4 decomposition to H2 and nanocarbons

The catalytic CH4 decomposition (CMD) over Fe-based catalyst is an economical and environmentally friendly way to produce Cox-free H2 and carbon nanotubes (CNTs). The Fe-loading was varied to study its influence on the catalytic performance. The highest H2 yield (82.25%) was obtained with a 12% Fe content where the activity of the catalyst did not decrease for 3 h on-stream. A higher Fe content causes the Fe dispersion to decrease, resulting in a reduced available surface area of active sites. Different techniques were used to characterise the fresh and spent catalysts i.e., ICP-AES, XRD, H2-TPR, SEM, TEM, and Raman spectroscopy. Plotting kinetic results as a function of 1/T, defines two different conversion ranges, being reaction rate controlled at low temperature and diffusion rate controlled at high temperature. For the reaction rate controlled regime, the Arrhenius equation provides an activation energy of 101.26 kJ/mol (Ea) and a pre-exponential factor of 393 kmol/s (A).

Fabrication of Mn3O4-CeO2-rGO as Nanocatalyst for Electro-Oxidation of Methanol

Recently, the use of metal oxides as inexpensive and efficient catalysts has been considered by researchers. In this work, we introduce a new nanocatalyst including a mixed metal oxide, consisting of manganese oxide, cerium oxide, and reduced graphene oxide (Mn₃O₄-CeO₂-rGO) by the hydrothermal method. The synthesized nanocatalyst was evaluated for the methanol oxidation reaction. The synergetic effect of metal oxides on the surface of rGO was investigated. Mn₃O₄-CeO₂-rGO showed an oxidation current density of 17.7 mA/cm² in overpotential of 0.51 V and 91% stability after 500 consecutive rounds of cyclic voltammetry. According to these results, the synthesized nanocatalyst can be an attractive and efficient option in the methanol oxidation reaction process.

N2O Hydrogenation on Silver Doped Gold Catalysts, A DFT Study

In this study, the full reaction mechanism for N₂O hydrogenation on silver doped Au(210) surfaces was investigated in order to clarify the experimental observations. Density functional theory (DFT) calculations were used to state the most favorable reaction paths for individual steps involved in the N₂O hydrogenation. From the DFT results, the activation energy barriers, rate constants and reaction energies for the individual steps were determined, which made it possible to elucidate the most favorable reaction mechanism for the global catalytic process. It was found that the N₂O dissociation occurs in surface regions where silver atoms are present, while hydrogen dissociation occurs in pure gold regions of the catalyst or in regions with a low silver content. Likewise, N₂O dissociation is the rate determining step of the global process, while water formation from O adatoms double hydrogenation and N₂ and H₂O desorptions are reaction steps limited by low activation energy barriers, and therefore, the latter are easily carried out. Moreover, water formation occurs in the edges between the regions where hydrogen and N₂O are dissociated. Interestingly, a good dispersion of the silver atoms in the surface is necessary to avoid catalyst poison by O adatoms accumulation, which are strongly adsorbed on the surface.