UltraCat

Heterogeneous catalysis, which is involved in about 80% of industrial processes, has a prominent role to play in the quest for clean energy technologies. A major challenge lies in the development of atom-efficient catalysts, i.e. with both maximum efficiency (activity, selectivity, stability) and minimum amount of rare and expensive materials (especially noble metals, which are used in many catalytic processes and in automotive converters). In recent years, due to the development of last-generation electron microscopies, a fast growing interest for so-called “single-atom catalysts”, i.e. catalysts constituted of metals atomically dispersed on a stabilizing support, is observed. Similarly to the “nano” wave which has drastically changed materials science and opened the way to a variety of applications, the additional downscaling may open a new era. As a matter of fact, subnanometric downsizing gives rise to a dramatic change in the electronic properties of metals, which in turn leads to promising catalytic performances. However, as synthesis and characterization of these materials are challenging, the works in this field are still restrained to a limited number of catalytic systems. The UltraCat project aims at the design and investigation of new catalysts based on metals “ultradispersed” in the form of subnanometric particles down to isolated atoms, supported on mesoporous oxides for reactions with high interest for clean-energy-production processes involving hydrogen. The related challenges will be the use of non-noble metals, the tuning of metal loadings so as to increase the catalytic yields without significant decrease of the metal dispersion, and the softening of reactions conditions (lower operating temperatures and pressures). The catalyst preparation methods envisaged in the project are both simple for implementation and original by making use of mixed-oxide and intermetallic alloy chemistry concepts through thermal post-treatments. The first considered reaction is the preferential oxidation of CO in H2 (CO-PROX), which allows ultimate purification of hydrogen for proton-exchange-membrane fuel cells. The second reaction is the hydrogenation of CO2 to methanol, which is a promising way of valorizing anthropogenic CO2 into a high-value platform molecule and energy carrier. Both reactions are known to benefit from a high intimacy between the metal and the support, making the ultradispersion approach relevant. The hydrogen sorption properties of the materials (adsorption, absorption, hydride formation), which are dispersion-dependent and strongly linked to catalytic ones (though often neglected), will be investigated in parallel to catalytic reactions. In order to better understand the dynamic gas-solid interaction phenomena involved in the reactions, and in turn guide the materials conception, the catalytic systems will be investigated by advanced in situ/operando techniques such as aberration-corrected environmental transmission electron microscopy, vibrational spectroscopies (infrared, Raman), and synchrotron X-ray spectroscopies (XAS, XPS). These methods will be complemented by materials and reaction modeling through computer-based simulations using the density functional theory (DFT) within rationalizing and predictive approaches. The UltraCat consortium covers all the above aspects in an interdisciplinary manner (chemistry / physics, catalysis / hydrogen sorption, experiment / theory) while relying on preexisting informal collaborations and promising preliminary results, which should favor the success of this project.