A catalyst for the oxidation of volatile organic compounds and carbon monoxide comprising manganese and alumina, such catalyst having been impregnated with a phosphorus compound. The presence of the phosphorus compound results in a significant oxidative conversion of both the volatile organic compounds and the carbon monoxide. The catalyst is especially useful for treating gaseous streams that emanate from industrial sources, such as wood pulp manufacturing plants. The manganese portion of the catalyst is preferably comprised of manganese compounds comprising a defect non-stoichiometric manganese oxide of the type .beta.-Mn.sub.3O.sub.4+x, wherein x has the value of 0.1.ltoreq.x.ltoreq.0.25 in respect to about 80 to about 95% of all manganese atoms, and manganese aluminate in respect to the balance of the manganese atoms. The alumina portion of the catalyst is preferably comprised of high temperature forms of alumina of the type comprising .alpha.-Al.sub.2O.sub.3 and (.alpha.+.delta.+.theta.)-Al.sub.2O.sub.3.