The quest for selective heterogeneous hydrogenation catalysts is state of the art research. We present a simple surface modification method for Pt/TiO 2 catalysts employing organic thiols for the liquid phase selective hydrogenation of 4-nitrostyrene. Our modified catalyst shows a 100% switch of selectivity to 4-aminostyrene at conversion levels close to 100%.

The three-phase hydrogenation of nitrobenzene catalysed by nanosized gold over titania was investigated in a slurry. Simultaneous in situ ATR-FTIR monitoring of the liquid phase and at the solid/liquid catalyst interface identified the species adsorbed on the catalyst and those in the liquid phase during the reaction. Nitrosobenzene was not detected analytically while the spectroscopic measurements strongly indicated phenylhydroxylamine as an intermediate reacting before desorbing from the catalyst surface. Under the same reaction conditions, azobenzene and hydrazobenzene were identified as intermediates during the hydrogenation of azoxybenzene to aniline. When nitrosobenzene or phenylhydroxylamine was alternately fed as reactant, azoxybenzene was produced via a disproportionation route. With the former, azoxybenzene was not further reduced by hydrogen because nitrosobenzene deactivated the catalyst. Combined with H(2) uptake, the spectroscopic measurements provided new insights into the reaction mechanism of the gold catalysed hydrogenation of nitrobenzene and an update of the corresponding kinetics.

The cerium oxidation state in ceria-doped Rh/Al 2 O 3 catalysts during the methane steam reforming (MSR) reaction was determined by in situ X-ray absorption spectroscopy and online mass spectrometry at 773 K. The catalysts were characterized by electron microscopy and X-ray diffraction. The oxidation states of rhodium and cerium during MSR are related. A total of 25% of Ce 4+ reduces to Ce 3+ under a CH 4 /H 2 O/He flow when the catalyst is active in MSR (773 K). A slight reoxidation occurs when the catalyst is sequentially exposed to steam diluted in helium at high temperatures, showing that only a small fraction of CeO 2−x may be involved in the water activation step by reoxidation. The main role of ceria during reaction, besides the activation of water, is to stabilize the structure of alumina by forming CeAlO 3 and to maintain the dispersion of rhodium. KEYWORDS: methane steam reforming, Rh/Al 2 O 3 catalysts, CeO 2 , Sm 2 O 3 , in situ X-ray absorption spectroscopy

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Controlling the particle size of supported metal catalysts is essential to achieving active, selective, and stable catalysts. High-resolution electron microscopy has revealed that large Au particles (∼8 nm), supported on titania and if multiple-twinned, broke up into small particles (2−3 nm) during liquid-phase hydrogenation. Multiple-twinned Au particles, obtained after gas-phase reduction of as-prepared Au/TiO 2 at elevated temperature, break up into smaller particles. EXAFS confirmed that the multiple-twinned particles were agglomerates of smaller particles. In contrast, calcination caused a strong interaction between Au and titania and the formation of mainly single crystalline Au particles (4 to 5 nm), which were relatively stable during liquid-phase hydrogenation. Reduction and calcination lead to gold particles that are fundamentally different.

An autoclave reactor was modified to perform simultaneously high energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD XAS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy measurements without altering the reactor design. This operando cell allows one to follow changes in the electronic and geometric structure of the catalyst with HERFD XAS and relate them to the simultaneously detected activity and reaction species with ATR-FTIR formed during the reaction in the liquid phase. The capability of the cell is demonstrated by two studies. The first shows the reduction of Au/CeO(2) precursors in different solvents. The second shows that mainly Au(0) is present in the hydrogenation of nitrobenzene over Au/CeO(2).