A metal contaminated spent catalyst or regenerated catalyst from a biomass conversion unit may be subjected to an ammonium wash in order to remove potassium. The ammonium wash may include ammonium sulfate, ammonium nitrate, ammonium hydroxide, ammonium acetate, ammonium phosphates, and mixtures thereof. Acidity and catalytic activity of the biomass conversion catalyst is restored by the removal of potassium contaminants.