The shape effect of TiO₂ in VO_x/TiO₂ catalysts for selective reduction of NO by NH₃

Abstract

Anatase TiO 2 nanosheets exposing 74% of {001} facets and nanospindles exposing 81% of {101} facets were hydrothermally synthesized with the aid of F and CH 3 COO -, respectively. Upon vanadia loading at a monolayer amount level, the {001} facets on TiO 2 nanosheets favored the deposition of octahedral vanadia species, but the {101} facets on TiO 2 nanospindles resulted in the formation of tetrahedral vanadia species. The shape effect of TiO 2 , in terms of its predominantly exposed crystal facets, on the catalytic performance of VO x /TiO 2 samples for selective reduction of NO with NH 3 was examined. The octahedral vanadia species on TiO 2nanosheets showed a significantly higher activity than the tetrahedral vanadia species on TiO 2 nanospindles.

Insights into Redox Dynamics of Vanadium Species Impregnated in Layered Siliceous Zeolitic Structures during Methanol Oxidation Reactions

“…Operando XANES/EXAFS studies allowed the identification of differences in vanadium site dynamics during redox cycles in Vbased mixed oxides [27] and binary V 2 O 5 /CeO 2 and ternary V 2 O 5 / CeO 2 /SiO 2 systems. [28] Recently, Ek et al [29] explored the facetdependent reactivity of VO x species on TiO 2 previously observed in the selective reduction of NO to NH 3 [30] by visualizing redox dynamic processes over (001) and (101) facets of the oxide applying combined atomic-resolution TEM and electron energy loss spectroscopy (EELS) under alternated oxidizing and reducing environments. By applying in situ spectroscopic [31][32][33] and atomic-resolution imaging [34][35][36] techniques to monitor redox properties under a reaction environment, new ways are opened to move towards a more complete understanding of the reactivity in oxide-catalyzed processes.…”

Three-dimensional morphology of anatase nanocrystals obtained from supercritical flow synthesis with industrial grade TiOSO4 precursor

“…All these structures consist of TiO 6 octahedra that are linked either by edge-or corner-sharing. All polymorphs are semiconductors, and they have found applications in catalysis, water purification, dye-sensitized solar cells, gas sensing and hydrogen production (Roy et al, 2013;Wang et al, 2014;Xu et al, 2015;Stefik et al, 2013;Shi et al, 2015). Since the exact properties of titania are highly dependent of the nanocrystal characteristics, there has been very broad research on developing effective synthesis methods (Cargnello et al, 2014).…”

“…Following the pioneering work of Yang et al (2008), various studies have reported the possibility of controlling the a-TiO 2 nanocrystal shape to possess a nano-cuboid shape [ Fig. 1(b)] by using hydrofluoric acid or other fluorinecontaining compounds as the morphology regulating agent (Han et al, 2009;Gu et al, 2012;Liu et al, 2009;Shi et al, 2015). Furthermore, synthesis of tetragonal a-TiO 2 nanorods with mainly exposed {100} facets Wen et al, 2007; [Fig.…”

“…One of the most frequently adopted procedures for characterization of the 3D morphology of a-TiO 2 nanocrystals is the application of the Scherrer equation to powder X-ray diffraction (PXRD) peak widths to estimate the volumeaveraged crystallite size along specific crystalline directions based on a pre-assumed model, i.e. truncated tetragonal bipyramid or nano-cuboid (Sutradhar et al, 2014;Yang et al, 2008;Shi et al, 2015). This technique is more likely to verify the morphology rather than reveal the morphology, and in many cases the Scherrer equation is also just applied on the strongest diffraction peak without considering instrumental and/or strain effects on the diffraction peak broadening.…”

Molten Salt Hydrates in the Synthesis of TiO2 Flakes

“…11−14 The reasons behind the versatility of TiO 2 lie in its intrinsic properties such as low cost, nontoxicity, chemical stability, acidity, specific surface area, and relatively good thermal stability. These properties of TiO 2 have led to the development of a variety of metal or metal oxide catalysts supported on TiO 2 surfaces that can be utilized in highly important catalytic reactions such as the selective NO x reduction, 15 hydrodesulfurization, 16 water–gas shift, 17 oxidative dehydrogenation, 18−20 and so forth. Besides thermal catalysis, TiO 2 finds wide applications in photocatalytic reactions due to its very good semiconducting properties.…”