Ultrathin alumina monolayers grafted onto an ordered mesoporous SBA-15 silica framework afford a composite catalyst support with unique structural properties and surface chemistry. Palladium nanoparticles deposited onto Al-SBA-15 via wet impregnation exhibit the high dispersion and surface oxidation characteristic of pure aluminas, in conjunction with the high active site densities characteristic of thermally stable, high-area mesoporous silicas. This combination confers significant rate enhancements in the aerobic selective oxidation (selox) of cinnamyl alcohol over Pd/Al-SBA-15 compared to mesoporous alumina or silica supports. Operando, liquid-phase XAS highlights the interplay between dissolved oxygen and the oxidation state of palladium nanoparticles dispersed over Al-SBA-15 towards on-stream reduction: ambient pressures of flowing oxygen are sufficient to hinder palladium oxide reduction to metal, enabling a high selox activity to be maintained, whereas rapid PdO reduction and concomitant catalyst deactivation occurs under static oxygen. Selectivity to the desired cinnamaldehyde product mirrors these trends in activity, with flowing oxygen minimising CO cleavage of the cinnamyl alcohol reactant to trans-β-methylstyrene, and of cinnamaldehyde decarbonylation to styrene.
Bibliographical noteNOTICE: this is the author’s version of a work that was accepted for publication in Catalysis today. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Parlett, CMA, Durndell, LJ, Machado, A, Cibin, G, Bruce, DW, Hondow, NS, Wilson, K & Lee, AF, 'Alumina-grafted SBA-15 as a high performance support for Pd-catalysed cinnamyl alcohol selective oxidation' Catalysis today, vol. 229 (2014) doi http://dx.doi.org/10.1016/j.cattod.2013.11.056.
Funding: EPSRC (EP/E046754/1; EP/G007594/2; EP/F009488/1; a Leadership Fellowship; and studentships); Diamond Light Source for beamtime (SP7668-1); Royal Society for the award of an Industry Fellowship; and Leeds EPSRC Nanoscience and Nanotechnology Research Equipment Facility (LENNF) (EP/F056311/1) .
- selective oxidation