Catalyst for catalytically removing nitrogen oxides at low temperature and preparation method thereof

Abstract

The invention provides a catalyst for catalytically removing nitrogen oxides at low temperature and a preparation method thereof. The catalyst is an iron-based molecular sieve with high iron content; the preparation method comprises: stirring and mixing the molecular sieve with an iron salt substance and at least one organic compound under the conditions of deionized water and at least one alcohol mixed solvent, and then drying Dry, calcined. After calcination to remove the organic compounds in the mixture, heat at 350-800°C for 2-6 hours in a reducing atmosphere, and then conduct passivation treatment in an air atmosphere. Compared with iron-containing molecular sieves without mixed solvents, organic compounds, heat treatment under reducing atmosphere and air passivation, this technology significantly increases the active sites of iron on molecular sieves, broadens the active range, and can be used at 125-500°C NO in temperature range x NH 3 ‑SCR conversion efficiency is above 90%.

Description

technical field [0001] The invention belongs to the technical field of environmental catalysis, and in particular relates to a catalyst for the low-temperature catalytic removal of nitrogen oxides and a preparation method thereof, and more particularly relates to a catalyst for the low-temperature catalytic removal of nitrogen oxides in diesel engine tail gas based on molecular sieve improvement and its preparation method. Background technique [0002] With the development of modern industry and the increase in the number of gasoline and diesel locomotives, the emission of nitrogen oxides is still one of the main environmental pollutants. These pollutions not only cause damage to the atmospheric environment (ozone layer hole, acid rain and photochemical smog, etc.), but also seriously endanger human health. Nitrogen-containing reducing agents such as ammonia (NH 3 ) or urea (CO(NH 2 ) 2 ) to remove nitrogen oxides (NO x ) into nitrogen by selective catalytic reduction, ...

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Problems solved by technology

[0004] The main method of synthesizing Fe-ZSM-5 catalyst is solid / liquid ion exchange and impregnation method at present, but there are following problems: the first, the iron content of Fe-ZSM-5 catalyst prepared by ion exchange method is not high at present, generally at 3% Below, and generally two or more times of exchange times are required for repeated roasting to achieve a higher iron content in the Fe-ZSM-5 catalyst, but repeated roasting is likely to cause defects in the crystal skeleton of the Fe-ZSM-5 catalyst, affecting the activity of the catalyst and stability

Second, although the existing impregnation method can make the Fe-ZSM-5 catalyst support a high iron content, most of its active sites exist on the surface of the molecular sieve, and they are clustered together in the form of oxides, resulting in the catalytic activity of the molecular sieve. Not active

However, in this method, due to the adjustment of the pH of the solution, the active metal elements are deposited on the "outer" or "inner" surface of the molecular sieve at specific sites, which will inevitably lead to a large amount of iron in the form of iron oxide, resulting in poor catalytic activity and selectivity.

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