Kinetics of CO2 hydrogenation to methanol over silica supported intermetallic Ga3Ni5 catalyst in a continuous differential fixed bed reactor

The methanol synthesis from CO2 hydrogenation is seen as a potential reaction for alternate fuel production as well as environmental clean-up. In this study, kinetics of methanol synthesis from CO2 hydrogenation has been investigated over Ga3Ni5/SiO2 catalyst. The catalyst was characterized by XRD, TEM-EDX, SEM, and ICP-MS techniques. The influence of different reaction variables like H2/CO2 ratio (3–9), temperature (423–523 K), and W/FAo (26.54 × 103 to 79.62 × 103 kg.s/kmolCO2) was studied at atmospheric pressure in a differential plug flow (PFR) fixed bed reactor. Two Langmuir-Hinshelwood models with different adsorption terms (competitive and non-competitive) were developed for methanol synthesis and reverse water gas shift (RWGS) reaction using the experimental data. Model discrimination by statistical analysis combined with physio-chemical constraints revealed that the competitive model is the best kinetic model. The model results revealed that the reactants, reaction intermediates, and products adsorb competitively over the same active sites on Ga3Ni5 surface. It was also found that the formate hydrogenation is the rate determining step for methanol synthesis with adsorbed atomic H2 and CO2 as the most abundant reaction intermediates. The kinetic model results were found consistent with the reported literature.