Monoclinic zirconia (m-ZrO2) supported Ru, Rh, Pt, and Pd nanoparticles with controlled sizes were prepared and examined in glycerol hydrogenolysis to propylene glycol and ethylene glycol at similar conversions in the kinetic regime. Their activity (normalized per exposed surface metal atom, i.e., turnover rate) and selectivity depend sensitively on the nature of the noble metals and their particle size. At a similar size (ca. 2 nm), Ru exhibited a greater turnover rate than Rh, Pt, and Pd, and the rate decreased in the sequence Ru ≫ Rh > Pt > Pd by a factor of about 25 (from 0.035 to 0.0014 mol glycerol (mol surface metal·s)−1) at 473 K and 6.0 MPa H2. Following such activity sequence, Ru was more prone to catalyze excessive cleavage of C–C bonds, leading to the formation of ethylene glycol and methane, while Pd exhibited the highest selectivity to cleavage of C–O bonds to propylene glycol. Similarly, larger Ru particles possessed higher glycerol hydrogenolysis activity concurrently with higher selectivities to ethylene glycol and especially methane at the expense of propylene glycol in the range of 1.8–4.5 nm. Analysis of kinetics and thermodynamics for the proposed elementary steps involving kinetically relevant glycerol dehydrogenation to glyceraldehyde leads to expressions of glycerol hydrogenolysis rate and selectivity to cleavage of C–O bonds relative to C–C bonds. Together with different effects of reaction temperature and atmosphere of H2 and N2 on the activity and selectivity for Ru/m-ZrO2 and Pt/m-ZrO2, these results suggest that the observed difference for different noble metals and particle sizes can be attributed to the difference in the strength of adsorption of glycerol and glyceraldehyde, derived from their different availability of unoccupied d orbitals.

A wide variety of hydrocarbon processes, catalytic or noncatalytic, involve the formation of carbon deposits, either on catalysts or on reactor (or engine/exhaust) surfaces. Therefore, researchers have developed a large array of catalysts to aid the combustion of these deposits. Recently, the mechanism of catalytic carbon oxidation and/or gasification has been the focus of research in an attempt to design better catalysts for carbon removal. With this approach, understanding the mechanism of formation of different types of carbon deposits is desired. Efforts undertaken for studying oxidation or gasification of various forms of carbon deposits are discussed in this review, along with the techniques used to study the mechanism of oxidation/gasification. The kinetics of catalyzed and noncatalytic carbon oxidation are described in detail. The effect of reactive gases such as NO x , water vapor, CO 2 , and SO 2 on the gasification behavior of carbon deposits is also discussed. Reaction rates of oxidation/gasification of carbon under different operating conditions have been calculated, allowing for a comprehensive overview of carbon removal reactivity.

Catalytic oxidation of alcohols often requires the presence of expensive transition metals. Herein, it is shown that earth-abundant Fe atoms dispersed throughout a nitrogen-containing carbon matrix catalyze the oxidation of benzyl alcohol and 5-hydroxymethylfurfural by O in the aqueous phase. The activity of the catalyst can be regenerated by a mild treatment in H . An observed kinetic isotope effect indicates that β-H elimination from the alcohol is the kinetically relevant step in the mechanism, which can be accelerated by substituting Fe with Cu. Dispersed Cr, Co, and Ni also convert alcohols, demonstrating the general utility of metal-nitrogen-carbon materials for alcohol oxidation catalysis. Oxidation of aliphatic alcohols is substantially slower than that of aromatic alcohols, but addition of 2,2,6,6-tetramethyl-1-piperidinyloxy as a co-catalyst with Fe can significantly improve the reaction rate.

The selective oxidation of 1,6-hexanediol with O 2 to product aldehydes and acids occurs readily in water over supported Pt nanoparticles. The initial turnover frequency of 0.54 s −1 (at 343 K and 1 MPa O 2 ) decreases significantly with reaction time because of product competitive adsorption and irreversible adsorption of unknown strongly bonded species. To identify the poisoning species, in situ surface-enhanced Raman spectroscopy (SERS) and solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy were applied in this work. In situ SERS during 1,6-hexanediol oxidation revealed an accumulation of di-σ-bonded olefinic species with features at ∼1150 and ∼1460 cm −1 on the poisoned Pt surface. Consistent with SERS, 13 C NMR spectroscopy of a Pt catalyst deactivated by oxidation of 13 C-labeled 1,4butanediol revealed a CC peak associated with ethylene. Molecules containing olefinic groups are 2 orders of magnitude more effective at competing for Pt surface sites in comparison to the aldehyde and acid products from alcohol oxidation. The poisoning olefinic species were generated by decarbonylation of product aldehyde (as revealed by head space analysis) and could be easily removed from the deactivated catalyst by mild treatment in H 2 .