Oxidative Dehydrogenation of Glycerol-Derived Secondary Alcohols over Pt Nanoparticles Supported on Silicas of Varied Mesoporosity

Previous work has established chemo-selective oxidative dehydrogenation of glycerol on platinum bismuth bimetallic nanoparticles dispersed on ordered mesoporous silicas (e.g., SBA-15). Under select conditions, mass transport limitations hamper the rate of reaction despite empirical predictions of the relevance of internal mass transfer limitations that do not vaticinate such effects. To determine the nature of these mass transfer limitations, several silica supports with varying micro- and mesoporosity were synthesized (i.e., nonporous silica, SBA-15, Si-xerogel, KIT-6, and mesocellular silica foam). The method of metal nanoparticle deposition was also altered to tune Pt particle size by using incipient wetness impregnation, solution deposition, and colloidal dispersion through sonication. After H₂ reduction at 573 K, the catalysts were used to oxidize 1,3 diethoxypropan-2-ol and 1,3 dimethoxypropan-2-ol in a 10 cm³ glass test-tube with flowing air (0.17 cm³ s^-1) supplied through a needle submerged in the reactant solution (typically 3.5 cm³), continuous stirring (~ 16.7 Hz), and heating (323.15-363.15 K). Liquid products were analyzed using an Agilent 6890 gas chromatograph equipped with a HP-5 column, an autosampler, and flame ionization detector. Initial trials of aerobic oxidation of 1,3-diethoxypropan-2-ol over Pt and PtBi supported on Si-xerogel showed that these Si-xerogel supported catalysts had rates up to two orders of magnitude higher than catalysts on SBA-15 support and less influence from mass transport based on higher apparent activation energies.