Nanoengineering heterogeneous catalysts for the selective hydrogenation of key agrochemical and industrial derivatives

Abstract

Selective hydrogenation through tailored catalysts for both agrochemical and commercial chemical precursors opens the potential for low energy and low waste production within both industries. For the purposes of this work, catalyst series with varying loadings of palladium nanoparticles were prepared upon both amorphous silica, and the structured mesoporous SBA-15. Full and extensive characterisations of both series were performed, and comparisons between the two made. For work focusing on agrochemical derivatives, research was done using the simplified reference chemical crotononitrile. A wide range of systematic screenings were performed to identify the effect of a variety of variables upon the activity and selectivity of the reaction These included the effect of metal loading, catalyst mass, temperature, hydrogen pressure, and perturbation. Results indicated a poor selectivity towards nitrile hydrogenation within mild conditions, with more notable results within higher pressures Key findings within the crotononitrile work highlighted a retardation effect within higher pressures. Extensive work including beam-time at the Diamond Light Source synchrotron allowed for the successful identification of palladium-hydride in-situ. As a result, a positive correlation was formed between hydride formation and the retardation of the nitrile selectivity due to its effect upon the active sites of the catalyst. For the work looking at the commercial aspect of selective hydrogenation, the conversion of cinnamaldehyde to cinnamyl alcohol was reviewed. Utilising the same catalyst series identified in previous research, a similar screening of reaction conditions and their effects upon the activity and selectivity were performed. With key comparisons to previous work within the group utilising platinum-based catalysts, it was concluded that palladium exhibited a much higher activity but at the cost of lowered selectivity towards aldehyde hydrogenation. Additionally, with previous work espousing the effect of alignment within cinnamaldehyde hydrogenation, it was noted that palladium was much less beholden to the effects of support polarity due to silanol species. Parallel work on sterically inhibiting moieties within benzaldehyde test reagents also highlighted a strong effect on catalytic activity due to poor metal-reagent surface alignment.