Microkinetic modeling of CO2 hydrogenation to methanol

June 1, 2023

Francesco Cannizzaro defended his PhD thesis at the department of Chemical Engineering and Chemistry on May 25th.

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Reducing the world’s dependency on fossil fuel energy and controlling CO2 emissions by developing renewable energies has become a crucial societal challenge. One of the most attractive strategies to reduce these emissions is to close the carbon cycle by recycling CO2 and transforms it into liquid fuels and chemicals. For his research, Francesco Cannizzaro studied CO2 hydrogenation to methanol and the importance of the reactive mechanism at the molecular level.

When it comes to managing CO2 emissions, its hydrogenation to methanol (CH3OH) is particularly attractive as the methanol product can be directly used as a fuel or employed as building block to produce a wide range of chemicals.

The desired groundbreaking catalyst required to convert CO2 and H2 into CH3OH still represents a significant challenge. Recently, metal-promoted indium oxide (In2O3) catalysts have emerged as promising candidates to assist CO2 hydrogenation to methanol. However, a thorough understanding of the reaction mechanism at the molecular level under reaction conditions, which is key to develop effective catalysts for large-scale applications, is lacking.

Models

In his PhD research, Francesco Cannizzaro developed extensive models to elucidate the active phase and catalytic mechanism of methanol synthesis from CO2 hydrogenation on metal-promoted In2O3 catalyst.

To achieve this, Cannizzaro used computational approaches used which rely on density functional theory calculations and microkinetic modeling to explore the kinetics of catalytic reactions.

Single atom

Cannizzaro investigated the effect of single atom (Ni, Pd, Pt, Rh) promoters in In2O3 catalysts, highlighting that these are not active for methanol synthesis and mainly produce CO. In addition, he explored the promoting effect of Ni in Ni-In2O3 catalysts showing that small clusters are active and selective for methanol synthesis from CO2, while single Ni atoms, either doped in or adsorbed on the In2O3 surface, mainly catalyze CO formation.

He also investigated a comprehensive reaction network of CO2 hydrogenation to CO, CH3OH and CH4 on a InNi(100) model surface. On this catalyst, methane and methanol formation are inhibited by high barriers resulting in CO being the preferred product. In addition, Cannizzaro looked at the mechanism of CO2 hydrogenation to CH3OH and CO over In2O3-supported InxNiy clusters (Ni8, In2Ni6 and In6Ni2). While Ni8-clusters are active and selective to methanol, introducing In atoms in the cluster results in higher barriers for hydrogenation of formate intermediates making methanol formation unfavorable. As a result, the selectivity shifts towards the CO by-product.

Title of PhD thesis: Microkinetic modeling of CO2 hydrogenation to methanol on Ni-In2O3 catalysts. Supervisors: Emiel Hensen and Ivo Filot.

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Barry Fitzgerald
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