Modified CHA molecular sieve and preparation method and application thereof

Abstract

The invention relates to a modified CHA molecular sieve, and a preparation method and application thereof, in particular to the application to the exhaust gas treatment of diesel vehicles, and belongsto the field of catalytic materials. The molar ratio of silica to alumina in the modified CHA molecular sieve is 24.5 to 36; the pore volume of the modified CHA molecular sieve is not less than 0.32cm<3> / g; the crystallinity of the modified CHA molecular sieve is not more than 5% lower than that of a pre-modified H-CHA molecular sieve, the initial CHA molecular sieve is subjected to ammonium ionexchange and first calcinations to prepare the pre-modified H-CHA molecular sieve, and then is subjected to acid treatment and alkali treatment to prepare the modified CHA molecular sieve. The crystallinity of the modified Cu containing CHA molecular sieve prepared by copper exchange of the modified CHA molecular sieve is high, thus the service life of the modified Cu containing CHA molecular sieve as a catalyst in the selective reduction of ammonia is prolonged; and the pore volume of the modified Cu containing CHA molecular sieve is large, more materials which can cause the blockage of catalyst pore channel and reduction of pore volume can be accommodated, and thus the service life of the catalyst is prolonged.

Description

technical field [0001] The application relates to a modified CHA molecular sieve and its preparation method and application, especially the application in the treatment of diesel vehicle tail gas, which belongs to the field of catalytic materials. Background technique [0002] Nitrogen oxides (NOx) are serious air pollutants, and diesel vehicle exhaust emissions are one of the main sources of NOx. In order to meet the escalating emission standards, the treatment of diesel vehicle exhaust has become increasingly important and urgent. Selective catalytic reduction of ammonia (NH 3 -SCR) is currently a widely used after-treatment strategy for diesel vehicle exhaust NOx. [0003] Copper-exchanged Cu-CHA molecular sieve is currently recognized as the most effective ammonia selective catalytic reduction (NH for short) for diesel vehicle exhaust treatment. 3 -SCR) catalyst. From the perspective of economy and convenience, diesel vehicle exhaust treatment NH 3 -The SCR process ...

AI Technical Summary

Problems solved by technology

The above various such as (NH 4 ) 2 SO 4 or NH 4 HSO 4 and CuSO 4 and other sulfur-containing compounds, along with NH 3 - The use of SCR catalyst gradually accumulates in the pores of Cu-CHA molecular sieve, reducing its pore volume, covering its acid sites, hindering the contact of reactants with active centers, and finally leading to catalyst deactivation

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