Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of secondary pollutants (e.g., tropospheric ozone, PAN (peroxyacetyl nitrate), and secondary organic aerosols) and photochemical smog. The emission of these pollutants has led to a large decline in air quality in numerous regions around the world, which has ultimately led to concerns regarding their impact on human health and general well-being. Catalytic oxidation is regarded as one of the most promising strategies for VOC removal from industrial waste streams. This Review systematically documents the progresses and developments made in the understanding and design of heterogeneous catalysts for VOC oxidation over the past two decades. It addresses in detail how catalytic performance is often drastically affected by the pollutant sources and reaction conditions. It also highlights the primary routes for catalyst deactivation and discusses protocols for their subsequent reactivation. Kinetic models and proposed oxidation mechanisms for representative VOCs are also provided. Typical catalytic reactors and oxidizers for industrial VOC destruction are further discussed. We believe that this Review will provide a great foundation and reference point for future design and development in this field.

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Recent Advances in the Catalytic Oxidation of Volatile Organic Compounds: A Review Based on Pollutant Sorts and Sources.

Catalytic oxidation of volatile organic compounds (VOCs) – A review

The design and development of efficient TiO 2 -based, hybrid, nanostructured photocatalysts has recently been receiving substantial attention for environmental remediation due to their excellent physiochemical properties. This article provides an overview of the synthesis strategies and characteristics of the next-generation TiO 2 -based hybrid photocatalysts, produced in combination with polymers (e.g., polyaniline, polypyrrole, polythiophene) and carbon nanomaterials (e.g., graphene, GO, CNT, carbon quantum dots, carbon nitride). The structural aspects, nanostructure formation process, parameters affecting catalytic activity, photocatalytic mechanisms and photocatalytic applications of TiO 2 -based catalysts for efficient photocatalytic degradation of gaseous/volatile organic pollutants in water/air are reviewed. Further, current research trends, means to increase catalytic performance and future prospects of high-performance TiO 2 -based hybrid photocatalytic materials, are briefly summarized.

Hybrid nanostructures based on titanium dioxide for enhanced photocatalysis

Two types (imine and boronate) of covalent organic frameworks (COFs) having a porphyrin unit have been synthesized. The two highly crystalline porphyrin COFs (COF-366 and COF-66) display excellent chemical and thermal stability and are permanently porous. Two-dimensional extended layered structures of the two COFs demonstrate very high charge carrier mobility values (8.1 cm2 V−1 s−1).

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Covalent Organic Frameworks with High Charge Carrier Mobility

Vanadia-titania catalysts are highly regarded for the control of industrial and domestic gas effluents. They are particularly used for the abatement of volatile organic compounds and for the removal of aromatic, polyaromatic and polychlorinated air pollutants like furans and dioxins. Here, mixed oxide catalysts are formed by non-hydrolytic condensation of chloride precursors with diisopropyl ether in non-aqueous medium. Calcination was applied to provoke the migration of the vanadium oxide toward the surface of the anatase particles, leading to well-spread vanadia species. The materials are made of mesoporous spherical particles of a few microns, themselves constituted by the aggregation of 10-25 nm sized particles. Their chemical composition is precisely controlled. The samples are characterized by ICP-AES, N-2-physisorption, XRD, XPS, SEM and TOF-SIMS. Their performances as total oxidation catalyst are evaluated in the deep oxidation of benzene, chosen as a model atmospheric pollutant. The activity of the materials compares well with that of catalysts prepared by classical wet impregnation. Along with the V surface concentration, the environment in which V surface species are located is identified as a key parameter. The superior activity of polymeric species as compared to isolated ones is shown. (C) 2009 Elsevier B.V. All rights reserved.

One-step non-hydrolytic sol-gel preparation of efficient V2O5-TiO2 catalysts for VOC total oxidation

This paper examines the use of TiO2 nanotubes (HNTs) as supports for V2O5 based catalysts in the total oxidation of chlorobenzene. The effect of the addition of SO42− onto the support is also discussed. Vanadium was introduced either by direct incorporation of V during the elaboration of the nanotubes (in situ elaboration), or by the impregnation of V on the surface of the supports (ex situ elaboration). The obtained catalysts have been characterized by means of ICP-AES, N2 adsorption–desorption at 77 K, XRD, DRIFTS, XPS, H2-TPR and NH3-TPD. We demonstrated that sulfating step highly improves the catalytic performances of V-HNTs catalysts. This is due to an increased global acidity and a higher reactivity of redox sites thanks to the electronic interaction between sulfated titania and VOx species. Moreover, it seems that the ‘in situ’ or ‘ex situ’ elaboration route of sulfated V-catalysts influences the environment of vanadium species. In particular, the ‘in situ’ route leads to a more efficient catalyst.

Elaboration and characterization of sulfated and unsulfated V2O5/TiO2 nanotubes catalysts for chlorobenzene total oxidation

Total oxidation of benzene and chlorobenzene with MoO3- and WO3-promoted V2O5/TiO2 catalysts prepared by a nonhydrolytic sol-gel route

For several years, the authors study VO
 x
 /TiO2 catalytic formulations in the context of the oxidative abatement of aromatics, possibly chlorinated, from polluted air. This paper revisits their main findings and understandings. Although VO
 x
 /TiO2 catalysts, when upgraded with Mo or W oxides, are already used in industrial applications, it is shown that the systematic investigation (i) of the reasons why optimized synthesis and formulations are indeed efficient, (ii) of the nature of the sites responsible for the adsorption of the pollutants and their catalytic transformation, and (iii) of the corresponding mechanisms, is a valuable approach to identify guidelines and strategies for further improving the catalysts. The origin of the beneficial effects brought by WO
 x
 and MoO
 x
 to VO
 x
 /TiO2, and by the use of a sulphated titania support, is addressed, as well as the impact on the catalysts behaviour and performances of molecules inevitably present in a combustion exhaust gas, like CO and NO
 x
 co-pollutants and water. The behaviours of a chloro-aromatic molecule, like chlorobenzene, and an oxygen containing-heterocyclic molecule, like furan and dimethylfuran, are then compared and discussed in the debate of their selection as representative model compounds for the catalytic abatement of dioxins. In this context, it is shown that strategies developed to improve the performances of VO
 x
 /TiO2 formulations to abate Cl-aromatics, could be detrimental for cyclic molecules containing O-heteroatom, as entire dioxins. Finally, an integrated view of the catalytic process is presented by envisaging the case of a complex mixture, closer to the real application of gaseous effluent cleaning.

Romain Delaigle

Papers

One-step non-hydrolytic sol-gel preparation of efficient V2O5-TiO2 catalysts for VOC total oxidation

Elaboration and characterization of sulfated and unsulfated V2O5/TiO2 nanotubes catalysts for chlorobenzene total oxidation

Total oxidation of benzene and chlorobenzene with MoO3- and WO3-promoted V2O5/TiO2 catalysts prepared by a nonhydrolytic sol-gel route

Revisiting the Behaviour of Vanadia-Based Catalysts in the Abatement of (Chloro)-Aromatic Pollutants: Towards an Integrated Understanding

Catalysts based on pillared clays for the oxidation of chlorobenzene