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.

/pdf/recent-advances-in-the-catalytic-oxidation-of-volatile-zw2c35dbg7.pdf

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

The present work elucidated the morphology and crystal-plane effects of nanoscale ceria on the activity of Ru/CeO2 catalysts toward catalytic combustion of chlorobenzene taken as a model of chlorinated aromatic hydrocarbons (CAHs) CeO2 nanorods (CeO2-r), nanocubes (CeO2-c) and nano-octahedra (CeO2-o) (enclosed by {110} and {100}, {100} and {111}, respectively) as supports, were prepared by wet impregnation The status and structure of Ru species is quite dependent on the enclosed various facets Ru/CeO2-r possesses much more Ru4+, oxygen vacancies and Ru–O–Ce bonds than Ru/CeO2-c and Ru/CeO2-o, indicating that there is a stronger interaction between Ru and CeO2-r The surface oxygen mobility and reducibility follow the order of Ru/CeO2-r > Ru/CeO2-c > Ru/CeO2-o The activity test of chlorobenzene oxidation shows that Ru/CeO2-r is more active than that of Ru/CeO2-c and Ru/CeO2-o, with T10% and T90% of 160 and 280 °C, respectively, which can be related to a larger number of Ru–O–Ce bonds, higher content of Ru4+ and surface oxygen mobility and reducibility These results confirm that the activity of Ru/CeO2 catalysts for CB oxidation is greatly affected by CeO2 shape/crystal plane

Morphology effect of Ru/CeO2 catalysts for the catalytic combustion of chlorobenzene

Mn-based oxide-mixed catalysts modified with Ce and La, which were prepared by complexation method, were tested in the catalytic combustion of chlorobenzene (CB) as a model of chlorinated aromatics. The characterization by XRD, XPS, TPR and Raman shows that the addition of Ce makes a large portion of Mn species enter CeO2 fluorite, leading to the formation of MnCeOx solid solution. The structure to be composed of MnOx and MnCeOx solid solution is highly active for CB oxidation due to the presence of a large amount of active oxygen species. The addition of La can promote the thermal stability of MnCeOx solid solution during calcination up to 750 °C, and accordingly the catalyst presents high activity. The study on reaction kinetics shows zero order on CB concentration in the presence of the catalysts except for MnCe-550, indicating that adsorption strength of Cl species produced during the reaction is critical to CB combustion because the adsorbed Cl species can decrease the reducibility of Mn species, thus the mobility of oxygen. Nevertheless, high activity, good selectivity and desired stability were observed over MnCeLa catalysts at 350 °C.

Effect of Ce and La on the structure and activity of MnOx catalyst in catalytic combustion of chlorobenzene

CeO 2 and Ru doped CeO 2 nanoparticles with small particle sizes (∼7 nm) and high surface area (∼100 m 2  g −1 ) were prepared by a simple precipitation/coprecipitation method and aqueous NaOH solution (10 wt%) as the precipitating agent, and characterized by XRD, N 2 adsorption, TEM/HRTEM, Raman, XPS and H 2 -TPR. The catalytic combustion of chlorobenzene (CB) was investigated for the first time. The results revealed that the Ru doped CeO 2 catalysts exhibit an outstanding catalytic activity ( T 90% below 250 °C) and stability (at least 82 h at 275 °C) for CB decomposition. The better stability of the Ru-CeO 2 catalysts can be ascribed to the inorganic chlorine species or dissociative Cl adsorbed on active sites can be removed rapidly via the Deacon process catalysized by RuO 2 component with extraordinary stability (limited chlorination and easier Cl 2 evolution).

Dai Qiguang

Papers

Catalytic combustion of chlorobenzene over Mn-Ce-La-O mixed oxide catalysts