H-2/D-2 Kinetic Isotope Effects in Methanol Synthesis on an In2O3 Catalyst

Indiumoxide (In2O3) has become a very promisingcatalyst in recent years for its high selectivity of CO2 hydrogenation to methanol, an ideal fuel for green energy. For rationaldesign of this catalytic system, further kinetics and mechanisticinsights into this reaction are demanded. Here, based on a recentlyoptimized c-In2O3 catalyst, we investigate H-2/D-2 isotope effects on the catalytic methanol synthesisreactivity up to 16 bar and 270 & DEG;C by online MS measurements,in both steady and transient states. In addition to a normal kineticisotope effect (R (H) > R (D), where R is the isotope-correspondingreaction rate), the Arrhenius plot yields a higher activation energy(E (a)) for D-2/CO2 thanfor H-2/CO2 (121.5 & PLUSMN; 5.8 vs 100.6 & PLUSMN;4.9 kJ & BULL;mol(-1)) inputs. The activation energiesremain almost constant at 8 and 16 bar, and the pressure dependencestudy confirms that the reaction rate is nearly linear to the totalinput pressure. Quantitative transient analysis of the exchanged D/Hisotopic species reveals a much smaller E (a) (61 & PLUSMN; 5.2 kJ & BULL;mol(-1)) for methanol formationfrom surface D/H species. The results also indicate that the activesurface is highly reduced by hydrogen and there is a high efficiencyof converting surface hydrogen to methanol. These new findings willhopefully provide useful information toward the rational design ofactive and stable catalysts based on In2O3 forCO(2) hydrogenation to methanol.

Automated summary

Indium oxide (In2O3) has shown great potential as a catalyst for the selective hydrogenation of CO2 to methanol, a green energy fuel. In this study, the H-2/D-2 isotope effects on the catalytic methanol synthesis were investigated using online MS measurements. The results revealed a higher activation energy for D-2/CO2 compared to H-2/CO2 inputs. The study also showed that the active surface is highly reduced by hydrogen and has a high efficiency in converting surface hydrogen to methanol.