Abstract
The mode of operation of titania-supported vanadia (VOx) catalysts for NOx abatement using ammonia selective catalytic reduction (NH3-SCR) is still vigorously debated. We introduce a new high surface area VOx/TiO2/SBA-15 model catalyst system based on mesoporous silica SBA-15 making use of atomic layer deposition (ALD) for controlled synthesis of titania and vanadia multilayers. The bulk and surface structure is characterized by X-ray diffraction (XRD), UV-vis and Raman spectroscopy, as well as X-ray photoelectron spectroscopy (XPS), revealing the presence of dispersed surface VOx species on amorphous TiO2 domains on SBA-15, forming hybrid Si–O–V and Ti–O–V linkages. Temperature-dependent analysis of the ammonia SCR catalytic activity reveals NOx conversion levels of up to ~60%. In situ and operando diffuse reflection IR Fourier transform (DRIFT) spectroscopy shows N–Hstretching modes, representing adsorbed ammonia and -NH2 and -NH intermediate structures on Bronsted and Lewis acid sites. Partial Lewis acid sites with adjacent redox sites are proposed as the active sites and desorption of product molecules as the rate-determining step at low temperature. The high NOx conversion is attributed to the presence of highly dispersed VOx species and the moderate acidity of VOx supported on TiO2/SBA-15.
Highlights
The emission of nitrogen oxides (NOx ) into the atmosphere, mainly from the electric-power industry and daily traffic, brings about a tremendous threat to the environment as well as human health.As one of the major atmospheric pollutants, NOx has attracted increasing attention in recent years.Selective catalytic reduction (SCR) of NOx with NH3 is proved to be the most effective technology for the removal of NOx from stationary and mobile sources [1]
An NH3 -SCR model catalyst was prepared by controlled deposition of titania and vanadia onto a mesoporous high surface area silica support by use of atomic layer deposition (ALD)
Compared to other catalysts with similar composition, the SBA-15-based catalyst used in the present study shows a better NH3 -SCR performance and a wider temperature window for operation
Summary
The emission of nitrogen oxides (NOx ) into the atmosphere, mainly from the electric-power industry and daily traffic, brings about a tremendous threat to the environment as well as human health.As one of the major atmospheric pollutants, NOx has attracted increasing attention in recent years.Selective catalytic reduction (SCR) of NOx with NH3 is proved to be the most effective technology for the removal of NOx from stationary and mobile sources [1]. The emission of nitrogen oxides (NOx ) into the atmosphere, mainly from the electric-power industry and daily traffic, brings about a tremendous threat to the environment as well as human health. Commercial vanadia-based ammonia SCR catalysts are typically based on vanadia and tungstia (or molybdena) on TiO2 anatase, but vanadia supported on TiO2 has been extensively studied as a model catalyst system [2,3,4]. It is known from the literature, that SCR activities depend on the vanadia structure and the support material [5,6,7].
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