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With heterogeneous catalysts, chemical promotion takes place at their surfaces. Even in the case of single-atom alloys, where small quantities of a reactive metal are dispersed within the main host, it is assumed that both elements are exposed and available to bond with the reactants. Here, we show, on the basis of in situ X-ray absorption spectroscopy data, that in alloy catalysts made from Pt highly diluted in Cu the Pt atoms are located at the inner interface between the metal nanoparticles and the silica support instead. Kinetic experiments indicated that these catalysts still display better selectivity for the hydrogenation of unsaturated aldehydes to unsaturated alcohols than the pure metals. Density functional theory calculations corroborated the stability of Pt at the metal-support interface and explained the catalytic performance as being due to a remote lowering of the activation barrier for the dissociation of H2 at Cu sites by the internal Pt atoms.

Abstract: First-principles calculations based on density functional theory have been performed to elucidate the reaction mechanism for ethylbenzene dehydrogenation and the role of CO2 in H removal. On the basis of the experimental information and theoretical prediction, three model surfaces with Fe-, ferryl- and O-termination are constructed to represent the active Fe2O3(0001) surface. The calculated results indicate that on all of the three surfaces the C–H activation in the methylene group followed by the dehydrogenation of the methyl group is kinetically more favorable. The energy barriers for ethylbenzene dehydrogenation are lowest on the O-terminated surface, but the generated styrene is adsorbed too strongly to be released. As CO2 decomposition and the formation of HCOO are hindered by the relatively high activation energies, CO2 cannot serve as the oxidant to recover the O- and ferryl-terminated surfaces to keep the redox cycle. At the steady state of the reaction the coupling mechanism dominates on the Fe-terminated surface, with the synergistic effect between ethylbenzene dehydrogenation and the reverse water–gas shift reaction. Since the energy barrier for the formation of COOH is comparable to that for H2 formation, both the one-step and two-step pathways are predicted to contribute to the coupling mechanism, although the former is more probable. [Copyright &y& Elsevier]

Abstract: DFT–GGA calculations have been used to study the chemisorption of CH x (x =0–3), C2H y (y =3–5) and C3H z (z =3–8) on Pt(111) at the coverage of 1/9 ML. The adsorption energies, favored binding sites and geometric parameters of adsorption configurations are determined. All the carbonaceous species are found to be adsorbed on Pt(111) with C atoms sp3-hybridized. The geometries of adsorption configurations have been compared with published experimental data to evaluate the reliability of our calculation method. The calculated adsorption energies of C1 species, ranked in descending order, are as follows, C>CH>CH2 >CH3, and the similar trend has been observed with respect to the chemisorption of C2 species. As for the C3 species, propylene prefers binding to the surface in the di-σ mode and the adsorption energy is calculated to be −0.93eV. The stepwise dehydrogenation of propane to propynyl (CCCH3) is investigated by calculating the change of reaction heat, which suggests that propylidyne (CCH2CH3) is the most stable species on Pt(111). Based on the adsorption energies and Brønsted–Evans–Polanyi (BEP) analysis, propyne is predicted to be the most likely starting point for the C–C scission. [Copyright &y& Elsevier]

The kinetic effects of co-feeding of dimethyl disulfide (DMDS) and hydrogen on propane dehydrogenation (PDH) over the Pt-Sn-K/Al 2 O 3 catalyst were investigated by the response surface method. The 3-level Box-Behnken design for 4 factors (reaction temperature, propene, hydrogen, and DMDS flow rate) was used to design the experiment. The initial propane conversion, propene selectivity, and coking amount were chosen as responses and the results were fitted by quadratic models. The fresh and coked catalysts were characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS), thermogravimetry (TG), N 2 physisorption, and Fourier-transform infrared spectroscopy (FT-IR). Analysis of variance (ANOVA) results showed that the DMDS flow rate is significant for propane conversion and coking amount while hydrogen flow rate is only significant for the conversion. By using the fitted model for the response surface, it is found that DMDS can significantly reduce the coking amount at the expense of propane conversion, and hydrogen weakly affects the selectivity and coking amount. The optimal conditions to achieve maximum conversion and selectivity and minimum coking amount are not consistent. The DMDS and hydrogen flow rate should be optimized to obtain the maximum economic profit out of the propane dehydrogenation (PDH) process., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)