Supported gold nanoparticles are very effective catalysts for the selective oxidation of glycerol which represents an important bio-derived feedstock. In this paper we report that the acid/base properties, especially the acid site density, of these catalysts are the key factor in tuning the selectivity. A range of supported AuPt catalysts have been prepared by sol immobilization using acidic (H-mordenite, SiO 2 , MCM-41, and sulfated ZrO 2 ) and basic (NiO and MgO) oxides as supports. In particular, using MCM-41 as the support, a high selectivity to glyceraldehyde, an important labile intermediate, was found.Catal. Sci. Technol. This journal is

A mixed oxide support containing Ce, Zr and Al was synthesized using a physical grinding method and applied in the oxidative dehydrogenation of propane using CO2 as the oxidant. The activity of the support was compared with that of fully-formulated catalysts containing palladium. The Pd/CeZrAlOx material exhibited long-term stability and selectivity to propene (during continuous operation for 140 h) which is not normally associated with dehydrogenation catalysts. From temperature-programmed desorption of NH3 and CO2 it was found that the catalyst possessed both acidic and basic sites. In addition, temperature programmed reduction showed that palladium promoted both the reduction and re-oxidation of the support. When the role of CO2 was investigated in the absence of gas-phase oxidant, using a Temporal Analysis of Products (TAP) reactor, it was found that CO2 dissociates over the reduced catalyst leading to formation of CO and selective oxygen species. It is proposed that CO2 has the dual role of regenerating selective oxygen species, and shifting the equilibrium for alkane dehydrogenation by consuming H2 through the reverse water-gas-shift reaction. These two mechanistic functions have previously been considered to be mutually exclusive.

The use of AuPd nanoparticles in catalysis is widespread, with the activity being attributed to their precise structural properties. We demonstrate the restructuring of AuPd nanoparticles under CO oxidation conditions using a combined XAFS/DRIFTS approach. The fresh catalyst exhibits PdO islands at the surface of the nanoparticles, which are reduced under reaction conditions, a process observed via both DRIFTS and Pd K-edge XAFS measurements. From the EXAFS analysis alone the nanoparticles were observed to have a Au rich core with an outer region of intimately mixed Au and Pd atoms. This structure was found to remain mostly unaltered throughout reaction. However, the DRIFTS spectra showed that although Au was present on the surface during the initial stages of reaction the surface rearranged just before light-off, and contained only Pd atoms thereafter. This study highlights the advantage of this combined approach, where both the surface structure and local environment of the constituent metals can be probed simultaneously, allowing a complete picture of the restructuring of these bimetallic particles to be obtained under reaction conditions.

Creating a new chemical ecosystem based on platform chemicals derived from waste biomass has significant challenges: catalysts need to be able to convert these highly functionalized molecules to specific target chemicals and they need to be economicalnot relying on large quantities of precious metalsand maintain activity over many cycles. Herein, we demonstrate how Pd/NiO is able to direct the selectivity of furfural hydrogenation and maintain performance at low Pd loading by a unique dual-site mechanism. Sol-immobilization was used to prepare 1 wt % Pd nanoparticles supported on NiO and TiO 2 , with the Pd/NiO catalyst showing enhanced activity with a significantly different selectivity profile; Pd/NiO favors tetrahydrofurfuryl alcohol (72%), whereas Pd/TiO 2 produces furfuryl alcohol as the major product (68%). Density functional theory studies evidenced significant differences on the adsorption of furfural on both NiO and Pd surfaces. On the basis of this observation we hypothesized that the role of Pd was to dissociate hydrogen, with the NiO surface adsorbing furfural. This dual-site hydrogenation mechanism was supported by comparing the performance of 0.1 wt % Pd/ NiO and 0.1 wt % Pd/TiO 2 . In this study, the 0.1 and 1 wt % Pd/NiO catalysts had comparable activities, whereas there was a 10fold reduction in performance for 0.1 wt % Pd/TiO 2 . When TiO 2 is used as the support, the Pd nanoparticles are responsible for both hydrogen dissociation and furfural adsorption and the activity is strongly correlated with the effective metal surface area. This work has significant implications for the upgrading of bioderived feedstocks, suggesting alternative ways for promoting selective transformations and reducing the reliance on precious metals.

Methoxy adsorbed on MoOx/Fe2O3 surfaces.

The catalytic performance of a series of 1 wt % Pd/C catalysts prepared by the sol-immobilization method has been studied in the liquid-phase hydrogenation of furfural. The temperature range studied was 25–75 °C, keeping the H2 pressure constant at 5 bar. The effect of the catalyst preparation using different capping agents containing oxygen or nitrogen groups was assessed. Polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and poly (diallyldimethylammonium chloride) (PDDA) were chosen. The catalysts were characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The characterization data suggest that the different capping agents affected the initial activity of the catalysts by adjusting the available Pd surface sites, without producing a significant change in the Pd particle size. The different activity of the three catalysts followed the trend: PdPVA/C > PdPDDA/C > PdPVP/C. In terms of selectivity to furfuryl alcohol, the opposite trend has been observed: PdPVP/C > PdPDDA/C > PdPVA/C. The different reactivity has been ascribed to the different shielding effect of the three ligands used; they influence the adsorption of the reactant on Pd active sites.

Monometallic and bimetallic tin-containing framework architectures have been prepared by hydrothermal methods. Structural and spectroscopic techniques were used to probe the nature of the solid-acid sites, at the molecular level, using a combination of XRD, DR UV-Vis, solid state MAS NMR ( 119 Sn, 27 Al and 31 P) and XAFS. The nature and strength of the solidacid sites were experimentaly probed by FT-IR spectroscopy using CD3CN as a probe molecule. To elucidate further the localstructure, the structural characteristics of the Sn sites were probed using DFT calculations, with a view to rationalising the experimental findings. These detailed structural and spectroscopic studies revealed the presence of multiple Sn environments, with the monometallic SnAlPO-5 catalyst displaying a greater number of tetrahedral Sn(IV) active centres. These framework Sn(IV) centres generated stong Lewis acid sites, when compared with their bimetallic Co-Sn analogue, thereby affording attractive possibilities for modulating catalytic reactivity. IntroductionTetrahedral (Td) sites in microporous solids are widely reported as catalytic active centres in selective oxidation and acidcatalysed transformations, 1-4 of which Ti in TS-1, 5 Fe in ZSM-5 6 and Co in AlPO-5 7 are significant examples. Controlling the nature of these active sites allows one to tune the Lewis 8 and Brønsted acidity, 9 and regulate redox 10 centres for oxidation catalysis. The addition of a second heteroatom allows for further optimisation of these properties, as well as influencing the coordination geometry of the initial heteroatom. [2][3][4] The incorporation of Sn into zeolitic 11 and non-zeolitic 1,4 architectures has received significant attention for its promising performance in Baeyer-Villiger oxidations. 11 The activity of these systems was correlated with the presence of Sn in Td sites, with well isolated Lewis acidic centres, which can be used for a wide range of catalytic reactions. [11][12][13] The synthetic findings were supported by a large number of characterization techniques, including DR UV-Vis, 119 Sn MAS NMR and in situ IR spectroscopy. 11,14 Although such materials could be expected to show significant catalytic functionality, the incorporation of Sn into AlPO-5 frameworks in Td sites is, however, very limited and poorly understood.This work focuses on the isomorphous substitution of P(V) with Sn (IV) within AlPO-5 using a modified hydrothermal preparation method. 4 Cobalt (Co 2+ /Co 3+ ) ions can be simultaneously introduced into the AlPO-5 architecture 2,3,15 by the substitution of (Al 3+ ) sites. Recently, a combined DFT and EXAFS study demonstrated the potential of effecting catalytic synergy in Co−Ti bimetallic nanoporous frameworks. 16 However, the prospects of introducing a relatively heavier element like Sn, alongside a redox transition-metal such as Co, could pave the way for probing bifunctional catalytic transformations. Nevertheless, the structural and spectroscopic features of such a system needs to be probed in meticulous detail...

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