CO2 hydrogenation to methanol is a key process for developing carbon-neutral energy systems. It allows for the storage of renewable energy in chemical form and the utilisation of distributed CO2. However, conventional thermocatalysis faces a significant challenge: the high temperatures required to activate CO2, which is kinetically inert, also promote the reverse water-gas shift (RWGS) side reaction. This severely reduces the selectivity for methanol.
Photothermal catalysis offers a promising approach by harnessing photoexcited charge carriers. Unfortunately, current systems rely heavily on noble metals, and distinguishing between photochemical and thermal effects remains a long-standing mechanistic challenge.
In this work, we have developed a non-noble-metal U-In2O3-CeO2 heterojunction catalyst via a facile, scalable one-step urea-assisted coprecipitation method. The optimised rod-shaped 1:1 In/Ce catalyst, with a type II heterojunction enabling efficient charge separation, achieves a benchmark methanol production rate of 1054.6 μmol g⁻¹ h⁻¹ with 53.1% selectivity under visible-light irradiation (400–800 nm) at 247.7 °C and ambient pressure, ranking among the highest-performing non-noble photothermal systems under comparable conditions.
A key element of our mechanistic investigation is the Hiden HPR-20 EGA mass spectrometer, which was coupled with an operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) exhaust line. This setup enabled real-time, simultaneous monitoring of gaseous reaction products and the evolution of surface intermediates under both dark and illuminated conditions. As a result, we were able to distinguish between photochemical and thermal effects of light illumination, which represents the core breakthrough of this work.
Figure 1 (right). HPR-20 EGA, Hiden Analytical.
By combining isotopic labelling, kinetic analyses, and DFT calculations, we have demonstrated that oxygen vacancies, surface hydroxyl groups, and the redox cycling of Ce³⁺/Ce⁴⁺ work together to activate CO2. This process drives a unique carbonate-mediated photochemical pathway, which differs from the traditional thermally accessible formate route. This light-driven mechanism reduces the apparent activation energy, suppresses the reverse water-gas shift (RWGS) side reaction, and enhances methanol production beyond what is achievable through thermal methods alone.
This research enhances our understanding of the mechanisms underlying photothermal catalysis and provides a scalable design strategy for sustainable solar-driven fuel generation.
Project Summary by: Ziyi Zhong, Professor of Chemical Engineering, Guangdong Technion Israel, Institute of Technology (GTIIT), 241 Da Xue Road, Shantou, Guangdong, 515063, China.
Paper Reference: Yao, D., Li, S., Qin, C., Lin, X., Wang, L., Zhang, C., Chen, Y., Zhong, Z. and Vogt, C. (2026). Decoupling photochemical and thermal pathways in photothermal CO2-to-methanol hydrogenation on In2O3-CeO2 heterojunctions. Chem Catalysis, 6(3), p.101627. DOI: 10.1016/j.checat.2025.101627.
Hiden Product: HPR-20 EGA.
