Low temperature SCR catalyst with hydrothermal stability for diesel vehicle exhaust gas purification and preparation method thereof

Abstract

The invention provides a low temperature SCR catalyst with hydrothermal stability for diesel vehicle exhaust gas purification. The chemical formula of the catalyst is WO3 / Ce<x>Zr<1-x>O2+Al2O3, and thecatalyst is prepared by loading tungsten on a composite oxide material with a general formula of Ce<x>Zr<1-x>O2+Al2O3, wherein 0<x<1, the mass fraction of Al2O3 in the composite oxide is 6-12%, and the mass fraction of WO3 in the catalyst is greater than 0 and less than or equal to 15%. A preparation method of the Al2O3 modified WO3 / CeZrO2 composite oxide NH3-SCR catalyst is as follows: a salt solution is prepared by a soluble cerium salt, a soluble zirconium salt and a soluble aluminum salt, and the composite oxide Ce<x>Zr<1-x>O2+Al2O3 is prepared by precipitating with a corresponding alkalisolution, and then tungsten is loaded to obtain the catalyst. The low temperature activity of the catalyst is maintained or even improved while the hydrothermal stability is improved, and the catalyst has a relatively low activity temperature and a relatively wide full conversion temperature window for NO<x> in diesel vehicle exhaust gases.

Description

technical field [0001] The invention belongs to the technical field of SCR catalyst catalysis, and in particular relates to a low-temperature purification and conversion motor vehicle exhaust NO x Gas non-vanadium based WO 3 / CeZrO 2 Composite oxide NH 3 -SCR catalyst. Background technique [0002] With the promulgation of increasingly stringent nitrogen oxide emission regulations around the world, nitrogen oxides (NOx) in lean-burn vehicle exhaust x ) purification has become one of the environmental problems that need to be solved urgently. NO x It can bring environmental problems such as acid rain, photochemical smog, greenhouse effect and ozone hole, and cause serious harm to human health and ecological environment. 95% NO in the atmosphere x It comes from motor vehicle exhaust (49%) and flue gas (46%) emissions from thermal power plants. Ammonia Selective Catalytic Reduction of NO x (NH 3 -SCR) is currently the most promising diesel vehicle exhaust NO x Purifi...

AI Technical Summary

Problems solved by technology

[0003] V 2 o 5 -WO 3 (MO 3 ) / TiO 2 A series of catalysts (i.e. vanadium-based catalysts) have been successfully applied to stage IV (National IV) and V (National V) diesel vehicles to purify their exhaust NO x , with the promulgation of the more stringent sixth stage (i.e. National VI) emission standards, this type of catalyst cannot meet the National VI and higher standards for diesel vehicle exhaust NO x emission requirements

Mainly because there are still some unavoidable shortcomings of vanadium-based catalysts: the effective working window (300-400°C) of this type of catalyst cannot adapt to the temperature range of diesel vehicle exhaust (175-550°C); 3 The non-selective oxidation of NO x The purification rate drops rapidly, and a large amount of greenhouse gas N is produced 2 O, leading to the main product N 2 The selectivity of the vanadium-based catalyst is significantly reduced, and it also causes secondary pollution to the atmosphere; the thermal stability of the vanadium-based catalyst is poor, V 2 o 5 Has strong biological toxicity

But WO 3 / CeZrAlO x The fresh activity of the catalyst (before aging) was significantly lower than that of WO 3 / CeZrO 2 catalyst, which is due to the amphoteric oxide Al 2 o 3 Doping reduces the active species CeO x and surface acid content (Haidi Xu, Shuang Liu, Yun Wang, etc., Applied Surface Science, 2018, 427:656-669)

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