NEXAFS CHARACTERIZATION AND REACTIVITY STUDIES OF BIMETALLIC VANADIUMMOLYBDENUM OXYNITRIDE HYDROTREATING CATALYSTS

The surface and bulk compositions of vanadium molybdenum oxynitride (V 2MoO1.7N2.4), prepared by temperature-programmed reaction (TPR) of van adium molybdenum oxide (V2MoO8) with ammonia, have been characterized using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The NEXAFS data were recorded at the K-edges of nitrogen and oxygen, the L-edge of vanadium, and the M-edge of molybdenum. The nitrogen K-e dge region of V-Mo oxynitride shows the characteristic NEXAFS features of early-transition-metal nitrides, although these features are diffe rent from those of either VN or Mo2N. Furthermore, comparison of the e lectron yield and fluorescence yield measurements also reveals that th e oxidation state is different for vanadium near the surface region an d for vanadium in the bulk, which is estimated to be 2.8 +/- 0.3 and 3 .8 +/- 0.3, respectively. The oxidation state of bulk molybdenum is al so estimated to be 4.4 +/- 0.3. The X-ray diffraction pattern shows th at the bulk phase of the bimetallic oxide is different from the pure m onometallic oxide phases but the oxynitride has a cubic structure that resembles the pure vanadium and molybdenum nitride phases. The V-Mo o xide as prepared shows a preferential orientation of [001] crystallogr aphic planes which is lost during the nitridation process. This shows that the solid state transformation V2MoO8 --> V2MoO1.7N2.4 is not top otactic. The hydrodesulfurization (HDS), hydrodenitrogenation (HDN), a nd hydrodeoxygenation (HDO) activities of V-Mo oxynitride are also com pared to those of either VN or Mo2N catalysts. The bimetallic V-Mo oxy nitride catalyst shows higher HDS, HDN, and HDO activities than those of the monometallic nitride catalysts.