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Cu/ZnO catalysts have been widely studied for the hydrogenation of carbon dioxide to methanol at atmospheric pressure. In the work described here, several interesting issues are highlighted that have rarely been considered previously. An extensive study of the influence of the calcination and reduction temperatures and the metal loading was carried out. The best conditions found for catalyst preparation were calcination at 350 °C and reduction at 200 °C. The role of the different oxidation states of copper (Cu2+, Cu1+, and Cu0) was proven in the methane and methanol formation. CuZn alloy formation was observed when a reduction temperature of 400 °C was used. The use of this alloy led to higher methanol selectivity at higher temperatures (>200 °C). Finally, the metal loading study confirm the dual-site nature of the methanol synthesis mechanism.

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The aim of the work described here was to evaluate the catalytic performance of palladium catalysts supported on zinc oxide (Pd/ZnO) in the hydrogenation of CO2 to obtain methanol at atmospheric pressure. The influence of the reduction temperature, calcination conditions, metal loading and Pd precursor on the catalytic performance was studied.

Metal-doped (Mn, Cu, Ni, and Fe) cobalt oxides were prepared by a coprecipitation method and were used as catalysts for the total oxidation of toluene and propane. The metal-doped catalysts displayed the same cubic spinel Co3O4 structure as the pure cobalt oxide did; the variation of cell parameter demonstrated the incorporation of dopants into the cobalt oxide lattice. FTIR spectra revealed the segregation of manganese oxide and iron oxide. The addition of dopant greatly influenced the crystallite size, strain, specific surface area, reducibility, and subsequently the catalytic performance of cobalt oxides. The catalytic activity of new materials was closely related to the nature of the dopant and the type of hydrocarbons. The doping of Mn, Ni, and Cu favored the combustion of toluene, with the Mn-doped one being the most active (14.6 × 10−8 mol gCo−1 s−1 at 210 °C; T50 = 224 °C), while the presence of Fe in Co3O4 inhibited its toluene activity. Regarding the combustion of propane, the introduction of Cu, Ni, and Fe had a negative effect on propane oxidation, while the presence of Mn in Co3O4 maintained its propane activity (6.1 × 10−8 mol gCo−1 s−1 at 160 °C; T50 = 201 °C). The excellent performance of Mn-doped Co3O4 could be attributed to the small grain size, high degree of strain, high surface area, and strong interaction between Mn and Co. Moreover, the presence of 4.4 vol.% H2O badly suppressed the activity of metal-doped catalysts for propane oxidation, among them, Fe-doped Co3O4 showed the best durability for wet propane combustion.

Palladium/zinc catalysts supported on carbon nanofibers (CNFs) have been used to study the catalytic performance in the hydrogenation of CO 2 to obtain methanol at atmospheric pressure. The carbon nanofiber support has an influence on the nature of the PdZn alloy formed. The effect of the Pd/Zn molar ratio on the PdZn alloy particle size was analyzed. Lower Pd/Zn molar ratio leads to higher PdZn alloy particle size, which was associated with higher selectivity toward methanol. The influence of the type of nanofiber (platelet or fishbone) on the catalytic behavior was also studied and compared with that of a conventional Pd/ZnO catalyst. The palladium/zinc catalyst supported on platelet nanofiber was considered to be a good candidate for the hydrogenation of carbon dioxide to methanol.

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