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A non‐spinel model for the structure of γ‐Al2O3, with 25 % of the Al3+ cations at tetrahedral positions, has been the subject of wide interest. However, 17O NMR measurements and, more recently, 27Al NMR measurements have shown that there are considerably more Al3+ cations at tetrahedral positions. This means that the Al3+ vacancies in γ‐Al2O3 are not at tetrahedral but at octahedral positions, as in isostructural γ‐Fe2O3 and in accordance with density functional theory predictions. This has consequences with regard to the surface structure of γ‐Al2O3, and thus, for catalysis. [ABSTRACT FROM AUTHOR]

Temperature‐programmed reduction of transition‐metal phosphate precursors is the most commonly used method for the preparation of transition‐metal phosphides (a new class of versatile metal catalysts), but the reduction processes are still not clear. Here we describe the construction of a temperature‐programmed reduction‐infrared spectroscopy apparatus (TPR‐IR) to analyze the gas flows during the reduction of nickel, molybdenum, and tungsten phosphates. PH3 and Pn+ species already appeared in the gas flows at low temperature (ca. 200 °C), and PH3 was involved in the formation of phosphides. The emission of PH3 and Pn+ during the reduction of the molybdenum and tungsten phosphates was smaller than that of the nickel phosphate. Ni2P drastically accelerated the formation of the PH3 and Pn+. These results explain why excess phosphorus is needed for the preparation of Ni2P, and also demonstrate that the TPR‐IR technique is an efficient method to understand the complex processes of catalyst preparation. [ABSTRACT FROM AUTHOR]

Preparation of Ni2P by temperature-programmed reduction (TPR) of a phosphate precursor is challenging because the P−O bond is strong. An alternative approach to synthesizing Ni2P, by reduction of nickel hexathiodiphosphate (Ni2P2S6), is presented. Conversion of Ni2P2S6 into Ni2P occurs at 200-220 °C, a temperature much lower than that required by the conventional TPR method (typically 500 °C). A sulfur-containing layer with a thickness of about 4.7 nm, composed of tiny crystallites, was observed at the surface of the obtained Ni2P catalyst (Ni2P−S). This is a direct observation of the sulfur-containing layer of Ni2P, or the so-called nickel phosphosulfide phase. Both the hydrodesulfurization activity and the selective hydrogenation performance of Ni2P-S were superior to that of the catalyst prepared by the TPR method, suggesting a positive role of sulfur on the surface of Ni2P-S. These features render Ni2P-S a legitimate alternative non-precious metal catalyst for hydrogenation reactions. [ABSTRACT FROM AUTHOR]