Abatement of NO.sub.x in exhaust gases

A process for selectively reducing oxides of nitrogen in a mixture of gases containing oxygen, reducible oxides of nitrogen, and nitrogen, which process comprises contacting in a reaction zone said mixture of gases and approximately the stoichiometric amount of added ammonia needed to reduce said reducible nitrogen oxides to nitrogen, said contacting being conducted at a temperature of 200.degree. C. to about 600.degree. C. with a spent commercial hydrocarbon conversion catalyst, said catalyst comprising a crystalline zeolite having a silica to alumina ratio of at least about 50 and selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-21, ZSM-23, ZSM-35, ZSM-38 and ZSM-48.

In a process for the fluid catalytic cracking of a petroleum fraction which comprises contacting said fraction in a cracking unit with a fluid cracking catalyst whereby forming cracked products and deactivated catalyst containing a carbonaceous deposit, separating said deactivated catalyst from said cracked products, passing said deactivated catalyst to a regeneration unit where it is contacted at elevated temperature with an oxygen-containing gas whereby forming regenerated catalyst and a flue gas contaminated with NO.sub.x, discharging said flue gas, and recycling said regenerated catalyst, the improvement which comprises:

• adding prior to said flue gas discharging step an approximately stoichiometric amount of NH.sub.3 to said flue gas and contacting the resultant mixture at 200.degree. C. to 600.degree. C. with a commercial, spent organic conversion catalyst, said catalyst comprising a crystalline zeolite having a silica to alumina ratio of at least about 50 and a Constraint Index of 1 to 12 whereby converting said NO.sub.x to an innocuous gas, and thereafter discharging said treated flue gas.

A method for pretreating prior to discharge to the atmosphere an industrial exhaust gas contaminated with NO.sub.x, which method comprises:

• forming at a temperature of at least about 200.degree. C. a mixture of said exhaust gas and added ammonia, said ammonia being added in an amount to satisfy approximately the stoichiometric requirement for reduction of the NO.sub.x by NH.sub.3 ;
• and
• contacting said mixture at 200.degree. C. to about 600.degree. C. and at a gas hourly space velocity effective to substantially reduce said NO.sub.x content with a spent organic conversion catalyst comprising ZSM-5 or ZSM-11 crystalline zeolite.

A process for pretreating prior to discharge to the atomosphere an industrial exhaust gas contaminated with an ecologically unacceptable amount of NO.sub.x, which method comprises forming at a temperature of at least about 200.degree. C. a mixture of said exhaust gas and a variable, controlled amount of added ammonia, said amount being effective to reduce said NO.sub.x content of said discharged gas to an acceptable level, and contacting said mixture at 200.degree. C. to at least about 600.degree. C. with a catalyst comprising a porous crystalline siliceous solid having a pore size of at least 5 A.U., a silica to alumina ratio of at least 20, an alpha value of at least about 10 to 250, and a Dynamic Response Index (DRI) of at least 20, thereby avoiding the discharge or excessive concentrations of both NO.sub.x and ammonia.

A process for controllably pretreating prior to discharge to the atmosphere an industrial exhaust gas contaminated with NO.sub.x, said process comprising:

• contacting, at a temperature of about 200.degree. C. to at least about 600.degree. C., a mixture of said exhaust gas, and added ammonia, with a solid inorganic acid catalyst comprising an acid-resistant porous crystalline siliceous solid having a silica to alumina ratio of at least 20 and that is deactivated for acid catalyzed reaction prior to said contact with said mixture, said crystalline silicate having a pore size of at least 5 Anstroms, said deactivation being effective to increase its Dynamic Rsponse Index (DRI) to at least 20 without substantially affecting the activity of said catlyst for selective catalytic reduction of NO.sub.x.