A structure made from catalyst for use in the separation of nitrogen oxides from combustion exhaust gases which contain dust. The catalytic structure has plates with spaces therebetween to carry a flow of the exhaust gas therethrough. The catalyst is constructed of individual ceramic plates. The abrasion or wear resistance of the plates is chosen such that the dust in the exhaust gases flowing through the spaces abrades the plate surface at a rate which is at least equivalent to the deactivation of the catalyst surface by action of the nitrogen oxides, which constantly provides a fresh catalyst surface for reaction with the nitrogen oxides. The movement of the exhaust gas through the catalytic structure carries the dust and abraded material along with it and out of the structure.

A catalyst useful for dehydrating an alkanolamine to form an alkylenimine is prepared by providing an aqueous or hydrofluoric acid solution of a tantalum or niobium compound, neutralizing this solution with ammonium hydroxide to precipitate the metal hydroxide, washing the precipitated metal hydroxide with water and subsequently dissolving it in an aqueous solution of a lower carboxylic acid, e.g. oxalic acid, applying the acid solution to a catalyst support to impregnate it with the metal hydroxide and finally drying and calcining the impregnated support to form the desired metal oxide catalyst. An alkaline earth metal oxide is optionally employed by impregnating the support with an aqueous solution of the alkaline earth metal hydroxide, preferably prior to the application of the catalyst.

A molded catalyst for fitting into a reactor vessel having an inlet and an outlet for a reactant gas, the catalyst having openings therethrough parallel to the direction of a reactant gas which is introduced into the reactor vessel from the inlet, the catalyst comprising: a wear-resistant front portion facing the inlet of the reactor vessel, and the remaining portion of the catalyst made so wear-susceptible as to have either: (a) a wearability of 2-10% in a shaking abrasion test wherein grinding particles having an average particle size of 1000 .mu.m and a Mohs scale of 9 are placed in the openings of the catalyst in an amount of 50% by volume based on the total volume of the openings, and the catalyst is shaken for three hours with an amplitude of 77 mm and a frequency of 320 per minute; or (b) a wearability of 7.5-35% in an air abrasion test wherein an air which contains silica particles having an average particle size of 40 .mu.m in amounts of 70 g/m.sup.3 is passed through in a reactor vessel including a rectangular parallelepipedic catalyst of 45 mm wide, 45 mm thick and 100 mm long so fitted thereinto that the catalyst extends longitudinally in the direction of the flow of the air for 30 min. at a superficial velocity of 40 m/sec. at the front portion of the catalyst.

In a method for treating a gas containing dusts therein under a monolithic catalyst consisting of a ceramic support which is substantially porous throughout the structure, and has active ingredients uniformly dispersed therein and passages therethrough parallel to the flow of the gas for allowing the gas to pass therethrough, the improvement in which the catalyst has the sintered front portion or has a vitreous coating on the front portion. Alternatively, the improvement in which a metal or sintered ceramic lid having openings therethrough is fixed onto the front face of the catalyst with the passages in alignment with the openings of the lid.

Hydrotreating catalyst containing one or more metal oxides and/or sulphides selected from Group VI-B and Group VIII of the Periodic Table supported on a porous refractory carrier, wherein the catalyst being in form of an angular extrudate with rounded edges.