Abstract: The deactivation rate of a catalyst used for the high temperature, high space velocity desulfurization of heavy oils is reduced by the incorporation in the catalyst of a small amount of a noble metal.

Abstract: A process for reducing the ash content and the content of metals present in used motor oils by contacting the used motor oil with an aqueous solution of ammonium sulfate and/or ammonium bisulfate under conditions to react with the metal compounds present to form separable solids. In another embodiment of the invention, the used motor oil after reaction with an aqueous solution of ammonium sulfate and/or ammonium bisulfate can be further treated with an adsorbent and then optionally hydrotreated to produce an oil product suitable as a fuel or as a feedstock for lubricating oil compositions.