CO-induced phenomena on supported metal nanoparticles

This Master’s Thesis is part of an ongoing collaboration between the Department of Chemistry at the University of Torino (UniTO) and the Catalyst Division of Chimet S.p.A., an Italian company based in Arezzo, renowned for the recovery and refining of precious metals. Established in 2003, this partnership is centered on the detailed characterization of catalysts used primarily in hydrogenation reactions, which are vital in industries such as petrochemicals, pharmaceuticals, and fine chemicals. These catalysts are typically based on precious metals—primarily palladium and platinum, but also ruthenium and other less noble metals—supported on activated carbons and metal oxides like alumina and silica. The primary goal of this collaboration is to optimize the preparation and application of catalysts by rationalizing how various preparation factors—such as metal loading, choice of support, pre-reduction treatments, and synthesis methods—affect the physical and chemical properties of the catalysts, which in turn influence their performance in catalytic reactions. For over a decade, Chimet S.p.A. has been collaborating with UniTO's Physical Chemistry of Surfaces and Interfaces group, which is known for its expertise in characterizing catalysts and materials with high surface areas. This collaboration has provided critical insights into the surface properties of supports, the dispersion and morphology of supported nanoparticles, and the transformations these materials undergo during catalytic processes. In the context of catalyst characterization, many techniques rely on carbon monoxide (CO) as a probe molecule to investigate the surface properties of metal nanoparticles. Recent studies, using a combination of gas-volumetry, adsorption microcalorimetry, and infrared (IR) spectroscopy, have shown that CO can induce surface roughening in Pd nanoparticles supported on alumina. Since surface and structural changes have a profound effect on catalytic performance, this thesis aims to extend the investigation to other metals and supports, with the goal of deepening our understanding of adsorbate-induced phenomena in industrial catalysts based on supported metal nanoparticles. The experimental work of this thesis was conducted on a series of catalysts prepared in the laboratories of Chimet S.p.A. The research focused on two main objectives. The first part of the study examined the effect of the support on adsorbate-induced phenomena. This was accomplished by performing CO volumetry and microcalorimetry on a palladium (Pd) catalyst supported on wood-derived activated carbon, comparing the results with earlier studies on Pd supported on alumina. The second part of the study focused on the influence of the metal, comparing palladium (Pd), platinum (Pt), and ruthenium (Ru) while keeping the alumina support constant. In addition to CO volumetry and microcalorimetry, the catalysts were further characterized using IR spectroscopy with CO pulses. This technique was employed to identify the different species formed during CO adsorption on the metal nanoparticles and to track their evolution as CO coverage increased.