Financial support of Generalitat Valenciana (Project Prometeo 2009/047), the Spanish Ministry of Economy and Competitiveness (Project CTQ2012-30703), and the co-financing of both projects by FEDER resources.

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Diesel soot combustion ceria catalysts

Oxygen vacancy (O-vacancy) is essential in catalytic oxidation but little is known about its insight. Herein, a series of MnOx-CeO2 catalysts with various Mn/(Mn + Ce) molar ratios were synthesized with citric acid complex method for O-vacancy study in soot catalytic combustion. The samples were characterized by X-ray powder diffraction (XRD), N2 adsorption/desorption, O2-temperature programmed desorption (O2-TPD), H2-temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and in situ Raman spectroscopy. It has been shown that MnOx(0.4)-CeO2 catalyst presented more O-vacancies, thus exhibiting the highest catalytic activities and redox properties. With the utilization of in situ Raman, two types of O-vacancies, including Frenkel-type oxygen vacancy (F OV) and intrinsic oxygen vacancy (I OV), were clarified. Furthermore, the transform relation between F OV and I OV was found. Those two types of O-vacancies favored to the migration and transformation of active species, enhancing further the oxidation-reduction cycle and the catalytic activity for soot oxidation. In addition, Mn4+/Mn3+(Mn2+), Olatt, Osur and Ce4+/Ce3+ were believed to play important roles in soot oxidation. Finally, evolution of O-vacancies was proposed, which is of significance for soot catalytic oxidation.

Evolution of oxygen vacancies in MnOx-CeO2 mixed oxides for soot oxidation

Oxophilicity and thiophilicity are widely used concepts with no quantitative definition. In this paper, a simple, generic scale is developed that solves issues with reference states and system dependencies and captures empirically known tendencies toward oxygen. This enables a detailed analysis of the fundamental causes of oxophilicity. Notably, the notion that oxophilicity relates to Lewis acid hardness is invalid. Rather, oxophilicity correlates only modestly and inversely with absolute hardness and more strongly with electronegativity and effective nuclear charge. Since oxygen is highly electronegative, ionic bonding is stronger to metals of low electronegativity. Left-side d-block elements with low effective nuclear charges and electronegativities are thus highly oxophilic, and the f-block elements, not because of their hardness, which is normal, but as a result of the small ionization energies of their outermost valence electrons, can easily transfer electrons to fulfill the electron demands of oxyge...

A Quantitative Scale of Oxophilicity and Thiophilicity.

Manganese oxide has been recognized as one of the most promising gaseous heterogeneous catalysts due to its low cost, environmental friendliness, and high catalytic oxidation performance. Mn-based oxides can be classified into four types: (1) single manganese oxide (MnOx), (2) supported manganese oxide (MnOx/support), (3) composite manganese oxides (MnOx-X), and (4) special crystalline manganese oxides (S-MnOx). These Mn-based oxides have been widely used as catalysts for the elimination of gaseous pollutants. This review aims to describe the environmental applications of these manganese oxides and provide perspectives. It gives detailed descriptions of environmental applications of the selective catalytic reduction of NOx with NH3, the catalytic combustion of volatile organic compounds, Hg0 oxidation and adsorption, and soot oxidation, in addition to some other environmental applications. Furthermore, this review mainly focuses on the effects of structure, morphology, and modified elements and on the rol...

Gaseous Heterogeneous Catalytic Reactions over Mn-Based Oxides for Environmental Applications: A Critical Review.

https://rua.ua.es/dspace/bitstream/10045/8188/1/JCAT08-291%5b1%5d_a.pdf

Combined removal of diesel soot particulates and NOx over CeO2–ZrO2 mixed oxides

This work aims at exploring the thermal ageing mechanism of Pt on ceria-based mixed oxides and the corresponding effect on the oxygen storage capacity (OSC) performance of the support material. Pt was supported on low-surface-area CeO2–ZrO2–La2O3 mixed oxides (CK) by impregnation method and subsequently calcined in static air at 500, 700 and 900 °C, respectively. The evolutions of textural, microstructural and redox properties of catalysts after the thermal treatments were identified by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and high-resolution transmission electron microscope (HRTEM). The results reveal that, besides the sintering of Pt, encapsulation of metal by the mixed oxides occurs at the calcination temperature of 700 °C and above. The burial of Pt crystallites by support particles is proposed as a potential mechanism for the encapsulation. Further, the HRTEM images show that the distortion of the mixed oxides lattice and other crystal defects are distributed at the metal/oxides interface, probably indicating the interdiffusion/interaction between the metal and mixed oxide. In this way, encapsulation of Pt is capable to promote the formation of Ce3+ or oxygen vacancy on the surface and in the bulk of support. The OSC results show that the reducibility and oxygen release behavior of catalysts are related to both the metal dispersion and metal/oxides interface, and the latter seems to be more crucial for those supported on low-surface-area mixed oxides. Judging by the dynamic oxygen storage capacity (DOSC), oxygen storage capacity complete (OSCC) and oxygen releasing rate, the catalyst calcined at 700 °C shows the best OSC performance. This evident promotion of OSC performance is believed to benefit from the partial encapsulation of Pt species, which leads to the increment of Ce3+ or oxygen vacancies both on the surface and in the bulk of oxides despite a loss of chemisorption sites on the surface of metal particles.

Qing Liang

Papers

Thermal ageing of Pt on low-surface-area CeO2-ZrO2-La2O3 mixed oxides : Effect on the OSC performance

Oxygen activation on Cu/Mn–Ce mixed oxides and the role in diesel soot oxidation

The catalytic activity of CuO–CeO2 mixed oxides for diesel soot oxidation with a NO/O2 mixture

Selective oxidation of soot over Cu doped ceria/ceria–zirconia catalysts

Structure and oxygen storage capacity of Pr/Nd doped CeO2-ZrO2 mixed oxides