The structural changes of γ-Al 2 O 3 , Ni/γ-Al 2 O 3 , and Pt/γ-Al 2 O 3 catalysts under aqueous phase reforming conditions (liquid water at 200 °C and autogenic pressure) are examined over the course of 10 h. The changes are characterized by X-ray diffraction, NMR spectroscopy, N 2 physisorption, pyridine adsorption followed by IR spectroscopy, and electron microscopy. It is demonstrated that γ-alumina is converted into a hydrated boehmite (AlOOH) phase with significantly decreased acidity and surface area. For metal-free γ-alumina, the transformation is completed within 10 h, whereas the presence of nickel and platinum particles significantly retards the formation of boehmite. In the beginning of the treatment, the surface area of γ-alumina increases, suggesting surface pitting and formation of small boehmite particles on the surface of γ-alumina. This process is followed by the formation of a compact crystalline boehmite phase. It is proposed that the metal particles affect the kinetics of this transformation by blocking specific surface hydroxyl groups that act as initial hydration sites. The transformation of γ-alumina into boehmite is accompanied by sintering of the supported metal particles.

Acid gases such as SO 2 and CO 2 are present in many environments in which the use of nanoporous metal− organic frameworks (MOFs) is envisaged. Among metal− organic frameworks, zeolitic imidazolate frameworks (ZIFs) have been extensively explored as membranes or adsorbents. However, there is little systematic knowledge of the effects of acid gas exposure on the structure of ZIFs, in particular the mechanistic aspects of ZIF degradation by acid gases as well as the effects of ZIF crystal topology and linker composition on their stability. Here we present a generalized and quantitative investigation of the kinetic and thermodynamic acid gas stability of a diverse range of ZIF materials. The stability of 16 ZIFs (of SOD, RHO, ANA, and GME topologies) under different environmentshumid air, liquid water, and acid gases CO 2 and SO 2 (dry, humid, and aqueous)is investigated by a suite of experimental and computational methods. The kinetics of ZIF degradation under exposure to humid SO 2 is studied in detail, and effective rate constants for acid gas degradation of ZIFs are reported for the first time. Remarkably, the kinetics of degradation of the diverse ZIFs correlate strongly with the linker pK a and ZIF water adsorption in a manner contrary to that expected from previous predictions in the literature. Furthermore, we find that the material ZIF-71 (RHO topology) shows much higher stability relative to the other ZIFs in humid SO 2 and CO 2 environments.

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A series of alumina-supported Fe-based catalysts is prepared via a dry impregnation method in the presence of a phosphorus source (phosphate salt) and then used for the catalytic dehydrogenation of propane. Specifically, supported catalysts with Fe:P molar ratios of 1:1, 2:1, and 3:1 are prepared and their chemical composition, textural properties, and redox properties are characterized with an array of techniques. In the nonoxidative dehydrogenation (PDH) of propane at 600 °C and atmospheric pressure, the most active catalyst (Fe:P ratio of 3:1) exhibits 15% propane conversion and >80% C 3 H 6 selectivity. The calculated activity is 9.9 mmol/(h g Fe ) (mass basis) or 13 μmol/(h m 2 ) (surface area basis), with a corresponding TOF of 19 h −1 . During the initial stages of reaction under PDH conditions, the precatalyst is reduced and Fe(0) species are generated, eventually giving way to iron carbide species. During this induction period, significant carbon is incorporated into the catalyst and propylene selectivity is low. Only after the iron carbide phase appears do the reactivity and selectivity achieve steady-state conditions with high propylene selectivity and good activity. The addition of the phosphorus source in the precatalyst is found to be important in obtaining a catalyst with superior performance.