Beta-type zeolite for scr catalyst and method for converting nitrogen oxide using the zeolite

Abstract

The NOx reducibility of an SCR catalyst using beta-zeolite is low after the hydrothermal aging, especially at a temperature below 300 DEG C. Besides, the SCR catalyst using ammonia has a problem of large irritant and toxic ammonia gas emission. An SCR catalyst using beta-zeolite in which the molar ratio of SiO 2 / Al 2 O 3 is from 20 to less than 40, the particle diameter determined by SEM is 0.35 [mu]m or more, the full width at half maximum (FWHM) of the X-ray diffraction peak for (302) is less than 0.30 DEG , and the amount of adsorbed NH 3 is 1 mmol / g or more, or has an amount of adsorbed NH 3 following hydrothermal aging of 0.4 mmol / g or more, demonstrates high catalytic activity for NOx reduction at low temperatures following hydrothermal aging while also demonstrating a low level of discharge of irritating ammonia in exhaust gas.

Description

technical field [0001] The invention relates to a high-performance SCR catalyst and β-type zeolite used in the catalyst. This application claims the priority of Japanese Patent Application No. 2006-262303 for which it applied to Japan on September 27, 2006, and uses the content here. Background technique [0002] Beta zeolite is known to be used for NO X Reduction catalysts, especially NO using ammonia as reductant X A reduction catalyst (typically a zeolite called "Selective catalytic reduction" called an SCR catalyst). (refer to patent document 1) [0003] NO X The reduction performance is reduced, especially at low temperatures below 300°C, the performance reduction is significant, and it cannot be used. The reason why the performance of the SCR catalyst using β-type zeolite deteriorates after hydrothermal durability treatment is mainly due to insufficient heat resistance of β-type zeolite, especially at low temperatures, has not yet been fully understood. . Perfor...

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Problems solved by technology

[0003] NO X The reduction performance is reduced, especially at low temperatures below 300°C, the performance reduction is significant, and it cannot be used

The reason why the performance of the SCR catalyst using β-type zeolite deteriorates after hydrothermal durability treatment is mainly due to insufficient heat resistance of β-type zeolite, especially at low temperatures, has not yet been fully understood.

Performance of existing literature reports and commercially available SCR catalysts using zeolite beta at 200°C after hydrothermal durability treatment X Reduction rate is less than 30%

(Patent Document 5) But even by this method, NO at 200°C X The reduction rate is still less than 30%, and expensive rare earths must be used

(Refer to Patent Documents 5 to 9) However, for the β-type zeolite used as an SCR catalyst, no NO after hydrothermal durability treatment has been proposed. X Beta zeolite with high reduction rate, especially NO at low temperature X β-type zeolite with high reduction rate

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