Search

• GVL hydroconversion proceeds over oxide-supported metal catalysts. • Selectivity is controlled together by acidic and metallic catalytic functions. • Hydroconversion of GVL can be steered to get either 2-MTHF or PA. • 2-MTHF formation proceeds via 2-hydroxy-5-methyl-THF intermediate. • The GVL ring is opened to pentenoic acid over Brønsted acid sites. The hydroconversion mechanism of γ-valerolactone (GVL) was studied over a Co/SiO 2 and a Pt/aluminosilicate catalyst. The reaction was carried out at 250 °C, 30 bar, and WHSV = 1 g GVL ·g cat. -1 h-1. The Co/SiO 2 catalyst had moderate hydrogenation activity and Lewis acidity, whereas the Pt/aluminosilicate catalyst had high hydrogenation activity and Brønsted acidity. Diffuse Reflectance Fourier Transform Spectroscopic (DRIFTS) results suggested that the GVL ring was bounded more strongly to the stronger acid Pt/aluminosilicate than to the weaker acid Co/silica catalyst. The Pt/aluminosilicate catalyst was substantiated to open the GVL ring in a protonation/deprotonation process giving pentenoic acid (PE) intermediate and pentanoic acid (PA) as main final product. Over Co/SiO 2 catalyst 2-methyl-tetrahydrofuran (2-MTHF) and pentanol were the major products of GVL conversion. It was substantiated that latter transformation proceeded in consecutive hydrogenation and dehydration steps via 2-hydroxy-5-methyl-tetrahydrofuran and 1,4-pentanediol (1,4-PD) intermediates. The oxygen atoms of GVL were shown to establish H-bonds with the silanol groups of the Co/SiO 2 catalyst. The ν CO frequency of the adsorbed GVL depends on the adsorption interaction of the GVL and the silica surface. Three distinct ν CO bands were distinguished by DRIFTS. Quantum chemical calculations gave the structures of the three adsorbed GVL species. Operando DRIFTS examination of the catalytic reaction suggested that in the structure that was activated for hydrogenation/hydrogenolysis both the ring and the carbonyl oxygen were bound to silanol groups. [ABSTRACT FROM AUTHOR]

Operando DRIFT analysis of the surface species observed on Fischer Tropsch catalysts at work has been performed under H 2 /CO syngas at 503 K. Decomposition of the evolution in the IR operando spectra has been done by chemometric analysis in order to depict the modifications occurring on the surface of the nanoparticles as a function of time on stream. Results obtained on three catalysts with different reducibility determined from temperature programmed reduction experiments are confronted in order to correlate the spectral observations to the cobalt surface atoms speciation. Attribution of the IR components in the 2100–1750 cm −1 range is confirmed on the basis of the chemometric decomposition. The component falling in the 2068–2064 cm −1 range is assigned to CO sorbed onto Co° surface atoms of partially H 2 -reduced nanoparticles. This component is found to progressively decrease as a function of catalyst time on stream which indicates a progressive reduction of the nanoparticles under syngas at 503 K. [ABSTRACT FROM AUTHOR]

Abstract: Experimental evidences show that it is possible to produce methane from an exclusively inorganic way using CO2 and H2 on a Rh/γ-Al2O3 catalyst at low temperature and atmospheric pressure. New insights on the mechanism of methanation are given. The first step of the mechanism in the methanation reaction could be the chemisorption of CO2 on the catalyst. The second step is the dissociation of CO2 into CO and O adsorbed on the surface. The third step is the reaction of dissociated species with H2. Adsorption, dissociation of CO2 and the reaction of dissociated species with H2 are evidenced by in situ DRIFT experiments. The reaction could occur between the adsorbed species. However a reaction between adsorbed species and gaseous hydrogen cannot be excluded. XPS shows that the CO2 oxidizes the catalyst and this oxidation deactivates the catalyst. The conversion of CO2 also increases with temperature. Methane is the unique hydrocarbon molecule formed and obtained with almost 100% selectivity. No other hydrocarbonated products have been observed. [ABSTRACT FROM AUTHOR]

Two supported Ru catalysts were prepared by the chemical vapor deposition of Ru3(CO)12 on MgO and SiO2 (MOCVD). TEM, XRD, and static H2 chemisorption measurements confirmed that the Ru particle size was about 2 nm on both supports. Using in situ DRIFT (diffuse reflectance infrared Fourier transform) spectroscopy at atmospheric pressure it was found that the adsorption of CO on the reduced samples is clearly influenced by the supports whereas the adsorption of CO on the oxidized Ru catalysts is essentially independent of the support. O2 chemisorption measurements showed that a thin RuO2 surface layer was formed on both catalysts under oxidizing conditions at room temperature. The observed C–O stretching frequencies were found to be in good agreement with HREELS and LEED data reported for the RuO2(1 1 0) single crystal surface. The catalytic activity was assessed under high-vacuum conditions using the TAP (temporal analysis of products) reactor by co-feeding CO and O2. These conditions ensured that heat and mass transfer limitations were absent. Both supported Ru catalysts were found to be highly active and stable under the CO oxidation conditions even down to room temperature. The deactivation of the catalysts observed at room temperature was reversible and independent of the support. The turnover frequencies (number of CO2 molecules per metal surface site per second) derived from steady-state measurements are in good agreement with data reported for the RuO2(1 1 0) single crystal surface under UHV conditions. Based on the results of the DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) and the kinetic measurements supported RuO2 is identified as the catalytically active phase. In addition, the turnover frequencies are in good agreement with data reported for Ru/SiO2 at atmospheric pressure. Thus, both the materials and the pressure gap were bridged successfully. [Copyright &y& Elsevier]