Morphology-Oriented ZrO₂-Supported Vanadium Oxide for the NH₃-SCR Process: Importance of Structural and Textural Properties

Abstract

ZrO 2 supports, with diverse morphologies (hollow sphere, star, rod, mesoporous), were produced using hydrothermal and evaporation-induced self-assembly methods. Zirconia-supported vanadium oxide catalysts were prepared by wet impregnation and used for the low-temperature selective catalytic reduction (SCR) of NO with ammonia. Characterization of catalysts includes N 2 physisorption, elementary analysis, X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction by H 2 , and temperature-programmed desorption of NH 3 . Significant differences in terms of activity are measured. 3 wt % V 2 O 5 supported on mesoporous ZrO 2 (V/MZ) presents excellent N 2 yields (>90%, in the 200−400 °C interval), with a wide operating temperature window (NO conversion > 95%, in the 225−425 °C interval), and less interesting performances were obtained when vanadium oxide is supported over stars, hollow spheres, and rods. Surface characterization showed a content of tetravalent vanadium ion, when supported, decreasing in the order of mesoporous > hollow sphere > star > rod. This order is in perfect agreement with the order of performance of the catalyst in the NH 3 -SCR reaction. The impact of tetravalent ion's presence on the surface is confirmed by diffuse reflectance infrared Fourier transform spectroscopy analysis, Brønsted acid sites generated on the surface, and the V 4+ -OH species involved in the reaction. The production of more important nitrite species over the tetragonal supported vanadium oxide catalyst could be another reason for the excellent NH 3 -SCR performance displayed by the V/MZ catalyst. When supported over monoclinic zirconia, like vanadium oxide over star-type morphology, the adsorbed NH 3 species (NH 4 + and coordinated NH 3 ) reacted with NO x adsorption species (nitrate) to form ammonium nitrate. Ammonium nitrate can be decomposed to N 2 and N 2 O (or NO 2 ). Thus, NO conversion curves and N 2 yield curves over tetragonal zirconia (MZ) at lower temperature were ahead of those over V/star ZrO 2 because of the higher V 4+ surface content and more active B acid sites associated with an easy formation of the nitrito intermediate.

Catalytic Reaction Mechanism of NO–CO on the ZrO2 (110) and (111) Surfaces

“…As zirconium dioxide (ZrO 2 ) has high thermal stability, excellent redox properties and an acid-basic site on its surface, it is a good catalyst and support material for various reactions, such as CO 2 methanation [3,4], water-gas shift [5,6], NH 3 selective catalytic reduction [7,8], and hydrodeoxygenation [9,10]. Especially, the transition metal oxide dispersed onto the surface of ZrO 2 exhibits powerful activity for NO reduction.…”

NH3-Selective Catalytic Reduction of NOx to N2 over Ceria Supported WOx Based Catalysts: Influence of Tungsten Content

“…Hence, the urgency to develop more efficient NOx abatement technologies is still essential. NOx removal includes three approaches [6]: (i) direct decomposition of NO x into O 2 and N 2 ; (ii) NO x storage reduction (NSR); and (iii) NO x selective catalytic reduction (SCR). NO x selective catalytic reduction (SCR) technology is classified according to the reducing agents used, such as hydrocarbons [7], oxygenated hydrocarbons [8,9], hydrogen [10], or ammonia (or urea) [11,12].…”

The Effects of the Crystalline Phase of Zirconia on C–O Activation and C–C Coupling in Converting Syngas into Aromatics

“…The crystalline phase of ZrO 2 can be controlled by the synthesis method. Different crystalline phases of ZrO 2 have diverse catalytic activities in many reactions [19][20][21][22][23][24][25][26][27]. In the conversion of syngas to isobutane, m-ZrO 2 with strong basicity performed higher reaction rate and selectivity to isobutene [24].…”