Understanding the Reduction of Transition‐Metal Phosphates to Transition‐Metal Phosphides by Combining Temperature‐Programmed Reduction and Infrared Spectroscopy

Abstract

AbstractTemperature‐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.