(36e) Challenges in Implementing in2O3 Catalyst for CO2 Hydrogenation to Methanol: H2o Effect and Stability
AIChE Annual Meeting
Monday, November 16, 2020 - 9:00am to 9:15am
The effect of additional moisture in the feed gas was studied on In2O3 and In2O3/ZrO2. Adding 0.1 mol% H2O significantly enhances CH3OH formation rate from 2.75 to 3.42 mol-kg-1-h-1 over In2O3/ZrO2. Similar enhancement is evident on In2O3. Characterization (STEM/EDS and CO2-TPD) confirms the preservation of In-Zr strong interaction in the presence of additional H2O and H2O-induced oxygen vacancies, which improves CO2 adsorption capacity. XPS reveals the formation of InOOH species due to H2O addition, which appears to correlate to H2O-dependant CH3OH enhancement. Density functional theory calculations demonstrate that adding H2O is found to facilitate surface InOOH formation, suppress COOH* pathway and thus CO formation, and promote CH3OH formation via HCOO* intermediate. However, excess H2O in the feed gas leads to aggregation of In species and reduction of surface In0 sites for H2 dissociation.
Long-term stability tests were conducted as well. After 100-h TOS, CH3OH formation rate on In2O3 drops significantly by 36%, while In2O3/ZrO2 remains stable. In situ X-ray absorption spectroscopy (XAS) results demonstrate that the stability originates from the interaction between In2O3/In2O3-x and ZrO2, which prevents deactivation through the over-reduction of In2O3 to In0. Structurally, ZrO2 plays a role in kinetically trapping In2O3/In2O3-x in an oxygen deficient state under reaction conditions.
These findings would be of importance for developing fundamental understanding of reaction chemistry involving in CO2-to-CH3OH and for shedding light on implementing In2O3 catalysts in practical process technology.