Weixin Zou

Engineering the NiO/CeO2 interface to enhance the catalytic performance for CO oxidation

In this work, NiO/CeO2 catalysts were synthesized with tunable CeO2 crystal facets ({110}, {111} and {100} facets) to study the crystal-plane effects on the catalytic properties. Kinetic studies of CO oxidation showed that NiO/CeO2 {110} had the lowest activation energy. Furthermore, the obtained samples were characterized by means of TEM, XRD, Raman, N2-physisorption, UV-Vis DRS, XPS, H2-TPR and in situ DRIFTS technologies. The results demonstrated that the geometric and electronic structures of the nickel species were dependent on the NiO/CeO2 interfaces, which had an influence on the synergetic interaction of absorbed CO and active oxygen species, and then the generation of the formate intermediate played an important role in the catalytic performance. The possible interface structures of nickel species on the CeO2 {110}, {111} and {100} surface were proposed through the incorporation model, suggesting that the advantageous NiO/CeO2 {110} interface facilitated CO adsorption/activation and active oxygen species formation, leading to the best catalytic performance.

Fe-Mn/Al 2 O 3 catalysts for low temperature selective catalytic reduction of NO with NH 3

A series of Fe-Mn/Al 2 O 3 catalysts were prepared and studied for low temperature selective catalytic reduction (SCR) of NO with NH 3 in a fixed-bed reactor. The effects of Fe and Mn on NO conversion and the deactivation of the catalysts were studied. N 2 adsorption-desorption, X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, H 2 temperature-programmed reduction, NH 3 temperature-programmed desorption, X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis and Fourier transform infrared spectroscopy were used to characterize the catalysts. The 8Fe-8Mn/Al 2 O 3 catalyst gave 99% of NO conversion at 150 ℃ and more than 92.6% NO conversion was obtained in a wide low temperature range of 90-210 ℃. XPS analysis demonstrated that the Fe 3+ was the main iron valence state on the catalyst surface and the addition of Mn increased the accumulation of Fe on the surface. The higher specific surface area, enhanced dispersion of amorphous Fe and Mn, improved reduction properties and surface acidity, lower binding energy, higher Mn 4+ /Mn 3+ ratio and more adsorbed oxygen species resulted in higher NO conversion for the 8Fe-8Mn/Al 2 O 3 catalyst. In addition, the SCR activity of the 8Fe-8Mn/Al 2 O 3 catalyst was only slightly decreased in the presence of H 2 O and SO 2 , which indicated that the catalyst had better tolerance to H 2 O and SO 2 . The reaction temperature was crucial for the SO 2 resistance of catalyst and the decrease of catalytic activity caused by SO 2 was mainly due to the sulfate salts formed on the catalyst.

Influence of preparation methods on the physicochemical properties and catalytic performance of MnOx-CeO2 catalysts for NH3-SCR at low temperature

This work examines the influence of preparation methods on the physicochemical properties and catalytic performance of MnO x -CeO 2 catalysts for selective catalytic reduction of NO by NH 3 (NH 3 -SCR) at low temperature. Five different methods, namely, mechanical mixing, impregnation, hydrothermal treatment, co-precipitation, and a sol-gel technique, were used to synthesize MnO x -CeO 2 catalysts. The catalysts were characterized in detail, and an NH 3 -SCR model reaction was chosen to evaluate the catalytic performance. The results showed that the preparation methods affected the catalytic performance in the order:hydrothermal treatment > sol-gel > co-precipitation > impregnation > mechanical mixing. This order correlated with the surface Ce 3+ and Mn 4+ content, oxygen vacancies and surface adsorbed oxygen species concentration, and the amount of acidic sites and acidic strength. This trend is related to redox interactions between MnO x and CeO 2 . The catalyst formed by a hydrothermal treatment exhibited excellent physicochemical properties, optimal cata-lytic performance, and good H 2 O resistance in NH 3 -SCR reaction. This was attributed to incorpora-tion of Mn n + into the CeO 2 lattice to form a uniform ceria-based solid solution (containing Mn-O-Ce structures). Strengthening of the electronic interactions between MnO x and CeO 2 , driven by the high-temperature and high-pressure conditions during the hydrothermal treatment also improved the catalyst characteristics. Thus, the hydrothermal treatment method is an efficient and environ-ment-friendly route to synthesizing low-temperature denitrification ( de NO x ) catalysts.

Preparation, characterization, and catalytic performance of high efficient CeO 2 -MnO x -Al 2 O 3 catalysts for NO elimination

A series of CeO 2 -MnO x -Al 2 O 3 mixed oxide catalysts (Ce:Mn:Al mole ratio = 6:4: x , x = 0.25, 0.5, 1, 2) were prepared by a simple one-step inverse co-precipitation method to investigate the influence of the incorporation of Al 3+ into CeO 2 -MnO x mixed oxides. CeO 2 -MnO x , CeO 2 -Al 2 O 3 , and MnO x -Al 2 O 3 mixed oxides, and CeO 2 were prepared by the same method for comparison. The samples were characterized by XRD, Raman, N 2 physisorption, H 2 -TPR, XPS, and in situ DRIFTS. The catalytic reduction of NO by CO was chosen as a model reaction to evaluate the catalytic performance. The incorporation of a small amount of Al 3+ into CeO 2 -MnO x mixed oxides resulted in a decrease of crystallite size, with the increase of the BET specific surface area and pore volume, as well as the increase of Ce 3+ and Mn 4+ . The former benefits good contact between catalyst and reactants, and the latter promotes the adsorption of CO and the desorption, conversion and dissociation of adsorbed NO. All these enhanced the catalytic performance for the NO+CO model reaction. A reaction mechanism was proposed to explain the excellent catalytic performance of CeO 2 -MnO x -Al 2 O 3 catalysts for NO reduction by CO.

Construction of hybrid multi-shell hollow structured CeO2–MnOx materials for selective catalytic reduction of NO with NH3

Hollow structured CeO2–MnOx hybrid materials with up to three shells were prepared successfully by using carbon spheres as the hard template. It was found that the shells could be well controlled by simply adjusting the calcination rate. Elemental mapping results showed Mn and Ce species exhibited a homogeneous spatial distribution and the existence of Mn could improve the diffusion of CeO2 into the carbon spheres during the construction of the multi-shell structure, suggesting the intensive cooperative interaction between Mn and Ce. When triple-shell CeO2–MnOx hollow spheres were used as a catalyst for selective catalytic reduction of NO with NH3, superior low-temperature catalytic performance was exhibited, compared with traditional CeO2–MnOx nanoparticles, single-shell and double-shell hollow spheres. Combined with XRD, H2-TPR and XPS characterization, it was indicated that the synergistic effects and surface active species enhanced by the special multi-shell CeO2–MnOx hollow structures could account for the excellent performances. The results of the present study shed light on the creation of complex and hybrid hollow structured materials for superior performance in catalysis fields, like NO reduction for environmental protection.

Synthesis of CrOx/C catalysts for low temperature NH3-SCR with enhanced regeneration ability in the presence of SO2

Chromium oxide nano-particles with an average diameter of 3xa0nm covered by amorphous carbon (CrOx/C) were successfully synthesized. The synthesized CrOx/C materials were used for the selective catalytic reduction of NOx by NH3 (NH3-SCR), which shows superb NH3-SCR activity and in particular, satisfactory regeneration ability in the presence of SO2 compared with Mn-based catalysts. The as-prepared catalysts were characterized by XRD, HRTEM, Raman, FTIR, BET, TPD, TPR, XPS and in situ FTIR techniques. The results indicated presence of certain amounts of unstable lattice oxygen exposed on the surface of CrOx nano-particles with an average size of 3 nm in the CrOx/C samples, which led to NO being conveniently oxidized to NO2. The formed NO2 participated in NH3-SCR activity, reacting with catalysts via a “fast NH3-SCR” pathway, which enhanced th NH3-SCR performance of the CrOx/C catalysts. Furthermore, the stable lattice of the CrOx species made the catalyst immune to the sulfation process, which was inferred to be the cause of its superior regeneration ability in the presence of SO2. This study provides a simple way to synthesize stable CrOx nano-particles with active oxygen, and sheds light on designing NH3-SCR catalysts with highly efficient low temperature activity, SO2 tolerance, and regeneration ability.

Ammonia promoted barium sulfate catalyst for dehydration of lactic acid to acrylic acid

The dehydration of lactic acid (LA) to acrylic acid over ammonia promoted barium sulfate was studied under various conditions. Interplanar spacing (d) calculated from the enlarged (121) diffraction peak of XRD patterns with the Bragg equation is influenced by preparation conditions, which determines the acid–base properties of the prepared barium sulfate. The present work focused on the preparation conditions such as alkaline agents, pH values and calcination temperatures, which affected the d value. It was found that aqueous ammonia was used as an alkaline agent at pH = 5 to synthesize barium sulfate with an appropriate d value, which displayed an excellent catalytic performance for LA dehydration to acrylic acid. In the presence of the prepared barium sulfate with an appropriate d value, the dehydration reaction of lactic acid proceeded efficiently, with 100% lactic acid conversion and ∼82% acrylic acid selectivity. The unprecedented catalytic performance is due to a balance between acidic sites and basic sites existing on the surface of the prepared catalyst. The catalyst is very stable for at least 24 h. The deactivation catalyst can be easily regenerated as it is calcined at 500 °C for 10 h under the air atmosphere.

Retracted article: Synthesis of Pt@TiO2@MnOx hollow spheres with high spatial charge separation efficiency for photocatalytic overall water splitting

We, the named authors, hereby wholly retract this Journal of Materials Chemistry A article due to the subsequent realisation that the O2 evolution rates reported and summarised in Fig. 5 cannot be repeated in the Valencia labs. However, the H2 evolution rates can still be reproduced. Because the oxidation products are mainly radicals or H2O2, we do not observe much O2 evolved. In addition, we also find that the O2 evolution rates seem to be related to the activity test equipment (the Hg lamp we used and the additives in H2O). Signed: Lichen Liu, Weixin Zou, Xianrui Gu, Chengyan Ge, Yu Deng, Changjin Tang, Fei Gao, Lin Dong and Avelino Corma, February 2014. Retraction endorsed by Liz Dunn, Managing Editor, Journal of Materials Chemistry A. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.