Experimental measurements of the conversion of m-cresol over Pt and Ru/SiO 2 catalysts show very different product distributions, even when the reaction is conducted at similarly low conversions and the same operating conditions (300 °C, 1 atm). That is, although ring hydrogenation to 3methylcyclohexanone is dominant over Pt, deoxygenation to toluene and C−C cleavage to C 1 −C 5 hydrocarbons prevail over Ru. For understanding the differences in reaction mechanisms responsible for this contrasting behavior, the conversion of mcresol over the Pt(111) and Ru(0001) surfaces has been analyzed using density functional theory (DFT) methods. The DFT results show that the direct dehydroxylation of m-cresol is unfavorable over the Pt(111) surface with an energy barrier of 242 kJ/mol. In turn, the calculations suggest that the reaction could proceed through a keto tautomer intermediate, which undergoes hydrogenation of the carbonyl group followed by dehydration to form toluene and water. At the same time, a low energy barrier for the ring hydrogenation path toward 3-methylcyclohexanone compared to the energy barrier for the deoxygenation path toward toluene over the Pt(111) surface is in agreement with the experimental observations, which show that 3methylcyclohexanone is the dominant product over Pt/SiO 2 at low conversions. By contrast, the direct dehydroxylation of mcresol becomes more favorable than the tautomerization route over the more oxophilic Ru(0001) surface. In this case, the deoxygenation path exhibits an energy barrier lower than that for the ring hydrogenation, which is also in agreement with experimental results that show higher selectivity to the deoxygenation product toluene. Finally, it is proposed that a partially unsaturated hydrocarbon surface species C 7 H 7 * is formed during the direct dehydroxylation of m-cresol over Ru(0001), becoming the crucial intermediate for the C−C bond breaking products C 1 −C 5 hydrocarbons, which are observed experimentally over the Ru/SiO 2 catalyst.

The influence of the support material of low loaded (< 2 V nm -²) vanadia catalysts on selectivities, activation energies and turn over frequencies in the oxidative dehydrogenation of propane and the combustion of propene was investigated. CeO 2 , TiO 2 , Al 2 O 3 , ZrO 2 and SiO 2 supported catalysts were prepared by saturation wetness impregnation in toluene. Characterization with temperature programmed reduction and Raman spectroscopy revealed a high dispersion of surface vanadia species for all investigated catalysts. The impact of heat and mass transfer limitations on the catalytic performance has been thoroughly excluded. Selectivities towards propene as well as activation energies strongly depend on the support material. For all catalysts, propene selectivity increases with temperature. Deconvolution of the reaction network of ODP into decoupled reactions of different reactants for at least three of the catalysts is not possible, because of a significant impact of the oxidation state of the catalyst on the reaction. Except for the CeO 2 supported catalyst, the contribution of the bare support material on the activity can be neglected.

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A combined experimental and theoretical comparative study of the hydrodeoxygenation (HDO) of anisole was conducted over Pt, Ru, and Fe metals. In the experimental part, an inert silica support was used to directly compare the catalytic activity and selectivity of the three metals at 375 ºC under H 2 flow at atmospheric pressure. In parallel, for density functional theory (DFT) calculations the close-packed Pt(111), Ru(0001), and Fe(110) surfaces were employed to compare the possible mechanisms on these metals. It was observed that over Pt/SiO 2 and Ru/SiO 2 catalysts, both phenol and benzene were the major products in a phenol/benzene ratio that decreased with the level of conversion. By contrast, over the Fe/SiO 2 catalyst, no phenol formation was detected, even at low conversions. The DFT results show that over all the three metal surfaces the dehydrogenation at the-CH 3 side group occurs before the CO bond breaking. This removal of H atoms from the-CH 3 group facilitates the activation of the aliphatic C alkyl-O bond. Therefore, it can be concluded that a common intermediate for the three metals is a surface phenoxy and the significant differences between the three metals is related to the reactivity of this surface phenoxy. That is, over Pt(111) and Ru(0001) the phenoxy intermediate is hydrogenated to phenol, which in turn, can undergo further HDO to form benzene. This result is in agreement with the experiments over Pt/SiO 2 and Ru/SiO 2 catalysts. Over these catalysts, both phenol and benzene are major products, with the selectivity to benzene increasing with conversion at the expense of phenol. In contrast, over the Fe(110) surface, the strong metal oxophilicity makes the direct cleavage of the CO bond in the surface phenoxy easier than

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VOx (1.4–1.7 V nm−2) supported on SBA-15, Al2O3, or TiO2 was studied before and after exposure to oxidative dehydrogenation of propane (ODP), and pure hydrogen or propane. After treatment, samples were quenched and frozen in quartz vials and characterized by using high-frequency electron paramagnetic resonance (HF-EPR). For SBA-15- and Al2O3-supported vanadia, V4+ sites were the most abundant paramagnetic species, whereas Ti3+ was dominant in TiO2-supported V2O5. For the quantification of paramagnetic reduced sites, Mn2+ was used as reference. The maximum relative numbers of reduced V4+ or Ti3+ sites were found to increase in the sequence SBA-15 (11 % V4+/V)

Silica (SBA-15) supported vanadium oxide was used for a kinetic study of the oxidative dehydrogenation of propane in a fixed bed reactor. Prior to this study, spectroscopic characterization using a variety of techniques such as FTIR spectroscopy, Raman spectroscopy, DR UV-Vis spectroscopy and X-ray Phototelectron Spectroscopy revealed the absence of bulk vanadia and a high dispersion of active surface sites for the investigated catalyst. The kinetic data evaluation was based on a formal kinetic approach. Calorimetric measurements were used to determine the heat of adsorption of propane on the catalyst. The data indicate that the primary combustion of propane is negligible. Reaction orders of one for the propane dehydrogenation and propene combustion indicate the participation of these species in the respective rate determining step. The zero reaction order determined for the catalyst reoxidation reveals a participation of lattice oxygen in this reaction step. Higher activation energies of propane dehydrogenation as compared to the propene combustion indicate the participation of the weaker allylic C-H bond of propene in the rate determining step of the propene combustion. This results in higher propene selectivites at elevated temperatures. Kinetic parameters, including apparent and real activation energies and the equilibrium constant of the propane adsorption allowed for a comparison with theoretical predictions and show a good agreement.

The oxidative dehydrogenation (ODH) of ethane on alumina-supported vanadia was investigated with the aim of understanding the effects of lattice oxygen and vanadium oxidation state on the catalyst ODH activity and ethene selectivity. Transient-response experiments were carried out with both a fully oxidized sample of 10 wt% VO(x)/Al(2)O(3) (7 V nm(-2)) and a sample that had been partially reduced in H(2). The experimental results were analyzed to determine the rate coefficients for ethane ODH, k(1), and ethene combustion, k(3). The rate of ODH was found to depend solely on the concentration of reactive oxygen in the catalyst, but not on the means by which this oxygen concentration was attained (i.e., by H(2)versus C(2)H(6) reduction). On the other hand, the ethene selectivity observed at a given concentration of active oxygen was found to depend on the composition of the reducing agent, higher ethene selectivities being observed when H(2), rather than C(2)H(6), was used as the reducing agent. It is proposed that the higher ethene selectivity achieved by H(2)versus C(2)H(6) reduction might be due to a lower ratio of V(4+) to V(3+) cations attained upon reduction in H(2) for a given extent of V(5+) reduction. This interpretation is based on the hypothesis that ethene combustion is initiated by C(2)H(4) adsorption on V(n+) cations present at the catalyst surface and that the strength of adsorption decreases in the order V(5+) > V(4+) > V(3+) consistent with the decreasing Lewis acidity of the cations.