Understanding the Reduction of Transition‐Metal Phosphates to Transition‐Metal Phosphides by Combining Temperature‐Programmed Reduction and Infrared Spectroscopy
Sheng Qiang, Xiang Li, R. Prins, Chunjing Liu, Qinglan Hao, Shaozhang Chen
Abstract
Abstract 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. PH 3 and P n+ species already appeared in the gas flows at low temperature (ca. 200 °C), and PH 3 was involved in the formation of phosphides. The emission of PH 3 and P n+ during the reduction of the molybdenum and tungsten phosphates was smaller than that of the nickel phosphate. Ni 2 P drastically accelerated the formation of the PH 3 and P n+ . These results explain why excess phosphorus is needed for the preparation of Ni 2 P, and also demonstrate that the TPR‐IR technique is an efficient method to understand the complex processes of catalyst preparation.