CO2 hydrogenation reaction over pristine Fe, Co, Ni, Cu and Al2O3 supported Ru: Comparison and determination of the activation energies

Abstract

Fe, Co, Ni and Cu are the main non-noble industrially significant catalysts in the CO2 and CO gas phase hydrogenation reaction towards hydrocarbons and alcohols. These catalysts are typically supported on metal oxides such as SiO2, TiO2, Al2O3 and ZnO, in order to maximize the activity towards the desired reaction. The role of the supporting material is to stabilize the catalytic nanoparticles and to prevent sintering at the elevated reaction temperatures and pressures. The supporting phase can improve the reaction activity or even have a crucial role in the reaction, as is the case, e.g. for the Methanol synthesis over Cu based catalysts on ZnO. Studying the metals without a supporting oxide phase is of capital importance for the fundamental understanding of the catalytic activity of the metal phase. Therefore, we investigated the pristine transition metals Fe, Co, Ni and Cu (diluted with silica glass beads to avoid sintering) towards their activity in the CO2 hydrogenation reaction and determined the activation energy. An Al2O3 supported Ruthenium catalyst with 0.5 mass percent of Ru loading was taken as reference system. It was found that Co, Ni and Ru/Al2O3 are mostly active in the Sabatier reaction, while Fe is active in the reverse water gas shift reaction. Cu as pristine metal shows no catalytic activity. C2+ hydrocarbons were formed on Co in low concentrations. For the calculation of the activation energy, the kinetically determined temperature range of the reaction is identified with a high resolution in time by means of a quantitative gas analysis method with an online mass spectrometer. The activation energy of the CO2 hydrogenation reaction was determined to be 50 kJ/mol over Fe, 77 kJ/mol over Co, 74 kJ/mol over Ni and 73 kJ/mol over the Ru/Al2O3 catalyst, indicating similar reaction pathways over Co, Ni and Ru/Al2O3 and a different reaction mechanism on Fe.

Mono- and bimetallic metal catalysts based on Ni and Ru supported on alumina-coated monoliths for CO2 methanation

“…The calculated apparent activation energies are displayed in Table 2. The activation energy for the Ni catalyst is similar to that reported in the literature for alumina-supported nickel catalysts (74 kJ mol −1 ), 20,[25][26][27] while that for the Ru monolith is slightly lower than that reported (51 vs. 73 kJ mol −1 ). The lower activation energy for the Ru catalyst suggests that the reaction is more favored over the Ru catalyst.…”

CO2 Hydrogenation over Unsupported Fe-Co Nanoalloy Catalysts

“…For the analysis of the products of the catalytic reaction, we applied a semi-quantitative method by means of mass spectrometry (MS), which allowed for the comparison of the activity and selectivity among the catalysts. This method is a variation of the quantitative analysis method we developed and described in detail in our previous work [19,20]. In comparison to that method, we accounted for the pressure fluctuations over the MS capillary by normalizing the intensity of the signal to a reference pressure, which was defined and the same for all experiments.…”

The Interplay between Structure and Product Selectivity of CO2 Hydrogenation

“…Specifically, CH 4 formation occurs via the formate hydrogenation and C−O bond scission in H 2 COH* or H 3 CO*. Among all pathways, the C−O bond scission should be a critical step and likely determines the overall CH 4 selectivity in CO 2 hydrogenation . In the case of Co 3 O 4 ‐0 h, the specific morphology improves the reducibility and lowers the V O formation energy.…”