Abstract: A method for purifying exhaust gases from a diesel engine is provided. The method utilizes a flow through type honeycomb catalyst having parallel through-cells and (1) a cross-sectional area at the inlet part of an exhaust gas cut by a face vertical to the direction of the through-cells of 10 to 100 cm.sup.2, preferably 20 to 80 cm.sup.2, per liter of the displacement of the engine,(2) an hydraulic diameter of the through-cells of 1.00 to 2.00 mm, preferably 1.10 to 1.40 mm, and(3) the percentage of open frontal area at the inlet part of the exhaust gas of 40 to 95%, preferably 50 to 85%.

Abstract: An improved process for producing maleic anhydride which comprises catalytically oxidizing benzene with a molecular oxygen-containing gas in the vapor phase in a multitubular heat-exchanger-type reactor. The process is characterized in thata catalyst-packed layer of the reactor is divided into a gas inlet side layer and a gas outlet side layer,the activity of the gas inlet side layer is controlled by adding at least one component selected from the group consisting of potassium, cesium, thallium and rubidium as a promoter or by decreasing the amount of phosphorus pentoxide (P.sub.2 O.sub.