PdZnO and PdInO cluster catalysts for CO2 hydrogenation to methanol

The catalytic conversion of greenhouse CO2 gas into methanol, a versatile commodity in the chemical industry and a sustainable energy carrier, is an attractive approach to mitigate the climate change by moving towards a more sustainable circular economy. Methanol is currently produced from fossil fuel syngas containing low amounts of CO2 over a Cu-ZnO-Al2O3 catalyst that is much less efficient when CO2 is the only carbon source. Catalysts based on Pd alloyed with post-transition metals such as Zn and In show promising CO2 hydrogenation to methanol activity, selectivity and stability that might be further enhanced if the metal-oxide interface and its role in the reaction mechanism is better understood. This lack of understanding largely results from the inherent complexity of the heterogeneous catalysts, which hinders active site investigation at reaction conditions. To overcome this challenge and determine more reliable structure-activity relationships, we are using an original approach to produce ligand-free nanoparticles of well-defined size and composition under ultra-high vacuum conditions and soft-land them onto carbon and oxide supports using Cluster Beam Deposition (CBD) technology. Notably, CBD produces catalysts, or spectator phases, simplifying the investigation of active phases and interfaces using techniques such as Transmission Electron Microscopy (TEM), Diffuse Reflectance Infrared spectroscopy (DRIFTS) and element-specific X-ray Absorption Spectroscopy (XAS).Series of bimetallic PdZn and PdIn nanoclusters with different stoichiometries will be produced by ablating alloy targets in a laser ablation cluster source and depositing them onto flat carbon paper that can be also be coated with oxides. CO2 hydrogenation activity of typically 10 ng of nanoclusters on flat supports will be tested in an in-house-build high pressure microreactor fitted with highly sensitive gas detection. The structural and electronic properties of the PdZnOx and PdInOx catalysts will be investigated ex situ using electron microscopy (SEM and TEM) as well as X-ray spectroscopy (XPS and XAFS). The most promising samples will be investigated in situ and operando using synchrotron-based X-ray absorption spectroscopy (XANES and EXAFS) under realistic CO2 hydrogenation conditions using a specially designed high-pressure reactor. Additionally, information of the reaction mechanism will be obtained using operando Modulation Excitation Spectroscopy (MES)-DRIFTS carried out in collaboration with our partners. The experimental results will guide theoretical modeling of the most promising catalyst to unravel possible active sites and reaction mechanism using DFT-based approaches.

Keywords:Physical Chemistry / Chemical Physics, Nanoparticles, CO2 hydrogenation, Material Characterisation, Catalysis

Disciplines:Surfaces, interfaces, 2D materials, Chemistry of clusters, colloids and nanomaterials, Physical chemistry of materials, Heterogeneous catalysis

Project type:PhD project