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Abstract: Hydrogenation of 1,3-butadiene over Au/ZrO2 catalysts with different gold loadings and calcination temperatures was reported. The catalysts were characterized in depth to understand their structure–property relationship. Gold oxidation states and surface hydroxyl groups, which were found to be sensitive to the gold loading, calcination temperature, and treatment with water, were shown to play vital roles in the hydrogenation activity of Au/ZrO2. Continued activity decrease was seen when the density of surface hydroxyl groups was lowered by elevating the pre-calcination temperature of ZrO2. Fully dehydroxylated Au/ZrO2 was essentially inactive, but became very active after partial regeneration of the hydroxyl groups by water treatment. Moreover, the activity of Au/ZrO2 increased with increasing Au3+/Au0 ratio. Isolated Au3+ ions at the support surface showed up to two orders of magnitude higher activity than Au0 atoms on Au particles. Several models are proposed to address the structural features of active sites for H2 activation in Au/ZrO2 catalysts. [Copyright &y& Elsevier]

The effects of active component (Ru, Rh, Pt, Pd, Ni, Fe) and support (CNTs, AC, Al2O3, MgO, ZrO2, TiO2) on the catalysis of ammonia decomposition were studied for the generation of COx-free hydrogen. It was shown that the Ru catalyst using CNTs as support exhibits the highest conversion of NH3. The performance can be further improved by modifying CNTs with KOH. According to the results of XRD, TEM, and chemisorption (CO and H2 as adsorbates) investigations, Ru dispersion is the highest on CNTs. In the range of 2–5 nm, the particle size of Ru on CNTs is the smallest among the supported Ru catalysts; the Ru particles on the metal oxides are in the 3–16 nm range. It seems that larger Ru particles are more active for NH3 decomposition in terms of TOF. Further investigation on the relationship between support basicity and catalytic activity disclosed that a support material of strong basicity is essential for high catalytic performance. In the N2-TPD studies of supported Ru catalysts, desorption was promoted over catalysts of strong basicity, suggesting that N2 desorption is the rate-determining step in ammonia decomposition. These results implied that it is possible to develop a highly efficient Ru catalyst for NH3 decomposition by using electron-conductive materials of strong basicity as support. [Copyright &y& Elsevier]

Abstract: Gas-phase dehydration of glycerol to produce acrolein was investigated at 315 °C over Nb2O5 catalysts calcined in the temperature range of 350–700 °C. The catalysts were characterized by nitrogen physisorption, TG-DTA, XRD, and n-butylamine titration using Hammett indicators to gain insight into the effect of calcination temperature on catalyst texture, crystal structure, and acidity. Calcination at 350 and 400 °C produced amorphous Nb2O5 catalysts that exhibit significantly higher fractions of strong acid sites at ( being the Hammett acidity function) than the crystallized Nb2O5 samples obtained by calcination at or above 500 °C. Glycerol conversion and acrolein selectivity of the Nb2O5 catalysts were dependent of the fraction of strong acid sites (). The amorphous catalyst prepared by the calcination at 400 °C, having the highest fraction of acid sites at , showed the highest mass specific activity and acrolein selectivity (51 mol%). The other samples, having a higher fraction of either stronger () or weaker acid sites (), were less effective for glycerol dehydration and formation of the desired acrolein. [Copyright &y& Elsevier]