High Surface Area VOx/TiO2/SBA-15 Model Catalysts for Ammonia SCR Prepared by Atomic Layer Deposition

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.

Rational Design of Mesoporous CuO–CeO2 Catalysts for NH3-SCR Applications Guided by Multiple In Situ Spectroscopies

“…Figure shows the wide-angle XRD patterns of the SBA-15-supported ceria or/and copper oxide samples. The broad diffraction peak at 2θ = 23° observed for template-free SBA-15 is assigned to the amorphous silica framework . After ceria loading, new peaks appear at 28.5, 33.2, 47.5, and 56.3° for both tfSBA-CeO 2 and asSBA-CeO 2 , which are readily attributed to crystalline CeO 2 .…”

“…The broad diffraction peak at 2θ = 23°observed for template-free SBA-15 is assigned to the amorphous silica framework. 27 After ceria loading, new peaks appear at 28.5, 33.2, 47.5, and 56.3°for both tfSBA-CeO 2 and asSBA-CeO 2 , which are readily attributed to crystalline CeO 2 . 23 After copper oxide loading, sample tfSBA-CuO shows a series of peaks at 32.67°(110), 35.63°(111), 38.90°(022), 48.83°(202), 53.60°(020), 58.24°(202), 61.59°(113), 66.5°(022), and 68.19°(220), corresponding to different planes of monoclinic CuO.…”

Controlling the dispersion of ceria using nanoconfinement: application to CeO2/SBA-15 catalysts for NH3-SCR

“…32 Since crystalline CeO2 cannot provide a sufficiently high specific surface area, especially after high-temperature aggregation, SBA-15 has been employed previously as a support material to disperse and stabilize CeO2 particles, 33 but also other NH3-SCRrelated materials. 34 In this contribution, we report how CeO2/SBA-15 catalysts were prepared by solid-state impregnation methods starting from bare and template-containing SBA-15, aiming at a mechanistic understanding of the synthesis. To monitor the calcination process in detail, in situ Raman, DRIFT, and DR UVvis spectroscopies were applied, revealing details of the transformation of the cerium precursor to the supported oxide.…”

Advanced Synthesis and Characterization of Vanadia/Titania Catalysts through a Molecular Approach

“…In order to reach this target, one has to begin from the first stage of the whole process, namely the catalysts synthesis. Two main routes are followed toward this direction: the use of model systems that provide full catalytic functionality but exhibit reduced chemical complexity [25][26][27][28]38,39] and the preparation of tailor-made catalysts using advanced synthesis methods [3,4]. The present study belongs to the second context.…”