New Catalysts for Hydroprocessing: Bimetallic Oxynitrides MI–MII–O–N (MI, MII=Mo, W, V, Nb, Cr, Mn, and Co): Part I. Synthesis and Characterization

Abstract

A new family of bimetallic oxynitride compounds, MI–MII–O–N (MI, MII=Mo, W, V, Nb, Cr, Mn, and Co), has been synthesized by nitriding bimetallic oxide precursors with ammonia gas via a temperature programmed reaction. The oxide precursors are prepared by conventional solid state reaction between two appropriate monometallic oxides. The synthesis involves passing NH3gas over the oxide precursors at a flow rate of 6.80×102μmol s−1(1000 cm3/min) and raising the temperature at a heating rate of 8.3×10−2K s−1(5 K/min) to a final temperature (Tf) which is held constant for a short period of time (thold). The oxynitrides thus obtained are pyrophoric and need to be passivated before exposing them to air. All these new bimetallic oxynitrides have a face centered cubic crystal structure and high values of surface area. The surface reactivation and the thermal stability of the materials are studied by temperature programmed reduction and this indicates that the compounds can be divided into three groups of different reducibility (high, medium, and low). Their surface activity and surface area are evaluated based on CO chemisorption and N2physisorption measurements. It is found that the chemisorbed CO number density correlates with the reducibility of the compounds.