High surface area tungsten oxynitride samples have been prepared by the temperature programmed reaction (TPR) of W0₃ with NH₃. All samples were characterized by X-ray diffraction (XRD), nitrogen physisorption, and CO chemisorption. In addition, some sample compositions were determined by elemental analysis. Samples were prepared at various heating rates (β), allowing a Redhead analysis to be carried out giving an activation energy of nitridation of 109 kJ mol⁻¹. A heating rate of 0.016 K S⁻¹ gave optimum synthesis conditions. Solid state intermediates were studied by interruption of the temperature program at various stages. No distinct suboxide phases formed along the synthesis path were found using XRD. An increase in surface area, CO uptake and nitrogen weight content, were found to occur as the reaction progressed. Reactivity experiments showed reasonable hydro deoxygenation (HDO) and hydrodenitrogenation (HDN) activities, but little hydrogenation (HYD) or hydrodesulfurization (HDS) activities.