Supported Cu catalysts for selective carbonyl hydrogenation - hydroxyacetone to 1,2-propanediol

Abstract

The global energy crisis and environmental challenges have driven significant research into biomass-based industrial processes. Developing biomass-derived platform chemicals, fundamental to the chemical industry, is a key focus. Hydrogenation plays a critical role in converting biomass to value-added chemicals, given the high oxygen content of biomass compounds. Heterogeneous catalysis is central to this process.

This thesis examines the selective hydrogenation of 1-hydroxypropan-2-one (HA) to 1,2-propanediol (PD) as a model reaction to study the hydrogenation of the carbonyl group in short-chain hydroxyketones. Copper-based catalysts, known for their affordability and selectivity in hydrogenating C=O bonds, were investigated, addressing challenges such as controlling copper oxidation states, their distribution on supports, and catalyst stability under reaction conditions.

The study prepared nine Cu/silica gel samples (S-samples) using various copper precursors (nitrate, acetate, basic carbonate) and solvents (water, ethanol, isopropanol). Results showed that the sample prepared with copper acetate and water as the impregnation solvent delivered the highest catalytic activity, which was associated to enhanced hydrogen localization.

Three samples supported over platelet carbon nanofiber (PCNF) were prepared with copper nitrate dissolved using different solvents (water, ethanol, isopropanol). PCNF-supported samples (C-samples) displayed better dispersion of Cu0 particles compared to silica gel, attributed to stronger interactions between copper and the surface functionalities of the PCNF. The S-catalysts exhibited higher activity which was linked to the presence of Cu+. However, they were prone to deactivation, attributed to Ostwald ripening. Conversely, the C-catalysts demonstrated excellent stability over 48 hours, attributed to the defective graphitic carbon structure of PCNF.

Modifications of the PCNF through acid and/or heat treatments influenced the distribution of functional groups on the support surface, impacting copper dispersion and stabilization. Optimal catalytic performance was achieved with a small percentage of Cu+, while excessive Cu+ content was associated with activity loss.

Lastly, the study established a linear relationship between the turnover frequency of HA hydrogenation and copper dispersion, showing the reaction's structure-sensitive nature. Cu(111) sites were identified as the primary active sites, and H2 adsorption emerged as the rate-determining step.

The findings highlight the importance of optimizing copper dispersion, defect density, and support interactions to enhance catalyst stability and activity. These insights contribute to advancing biomass conversion technologies for sustainable chemical production.