Mechanistic Insight into the Promotion of the Low-Temperature NH3-Selective Catalytic Reduction Activity over MnxCe1-xOy Catalysts: A Combined Experimental and Density Functional Theory Study.

CeO2 has attracted much attention in the field of selective catalytic reduction of NO with NH3 (NH3-SCR). However, poor low-temperature activity and a narrow operation window restrict the industrial application of Ce-based oxide catalysts. Herein, the low-temperature NH3-SCR activity of Ce-based oxide catalysts was dramatically improved by Mn doping, and the mechanism was elucidated at the atomic level by experimental measurements and density functional theory calculations. We found that the addition of Mn significantly promoted the formation of surface oxygen vacancies. The oxygen vacancies easily captured O2 in air and formed active oxygen species (superoxide and peroxide) on the surface. The surface active oxygen species efficiently oxidized NO into NO2 and then facilitated the "fast SCR" reaction. This study provides atomic-level insights into the promotion of the NH3-SCR activity over Mn-Ce composite oxides and is beneficial for the development of low-temperature Ce-based catalysts.

Insight into the Promotion Effect of Trace Pd Doping on the Catalytic Performance of Ag/Al2O3 for C3H6-SCR of NOx.

The mechanistic cause of the enhancement of the C3H6-SCR activity of Ag/Al2O3 by trace Pd doping and the corresponding structure-property relationship were investigated. Pd doping enhanced the water resistance of Ag/Al2O3 for C3H6-SCR by changing the reaction pathway. Under wet conditions, a series of in situ DRIFT studies indicated that the production of an active acetate intermediate on Ag/Al2O3 was suppressed during the partial oxidation of C3H6, while trace Pd doping promoted the formation of another active intermediate, an enolic species. Furthermore, a pathway for the formation of enolic species by the reaction of acrylate with hydroxyl species was proposed. DFT calculations revealed that the surface of Ag clusters was easily covered by hydroxyl in the presence of water vapor, which could inhibit the formation of acetates. Doping with Pd facilitated the activation of acrylate which might further react with hydroxyl species to form enolic species. These findings can be helpful for the future design of efficient HC-SCR catalysts.

Advances in emission control of diesel vehicles in China.

Diesel vehicles have caused serious environmental problems in China. Hence, the Chinese government has launched serious actions against air pollution and imposed more stringent regulations on diesel vehicle emissions in the latest China VI standard. To fulfill this stringent legislation, two major technical routes, including the exhaust gas recirculation (EGR) and high-efficiency selective catalytic reduction (SCR) routes, have been developed for diesel engines. Moreover, complicated aftertreatment technologies have also been developed, including use of a diesel oxidation catalyst (DOC) for controlling carbon monoxide (CO) and hydrocarbon (HC) emissions, diesel particulate filter (DPF) for particle mass (PM) emission control, SCR for the control of NOx emission, and an ammonia slip catalyst (ASC) for the control of unreacted NH3. Due to the stringent requirements of the China VI standard, the aftertreatment system needs to be more deeply integrated with the engine system. In the future, aftertreatment technologies will need further upgrades to fulfill the requirements of the near-zero emission target for diesel vehicles.

Promotion effect of H2 on ethanol oxidation and NOx reduction with ethanol over Ag/Al2O3 catalyst.

The catalytic partial oxidation of ethanol and selective catalytic reduction of NOx with ethanol (ethanol-SCR) over Ag/Al2O3 were studied using synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (PIMS). The intermediates were identified by PIMS and their photoionization efficiency (PIE) spectra. The results indicate that H2 promotes the partial oxidation of ethanol to acetaldehyde over Ag/Al2O3, while the simultaneously occurring processes of dehydration and dehydrogenation were inhibited. H2 addition favors the formation of ammonia during ethanol-SCR over Ag/Al2O3, the occurrence of which creates an effective pathway for NOx reduction by direct reaction with NH3. Simultaneously, the enhancement of the formation of ammonia benefits its reaction with surface enolic species, resulting in producing -NCO species again, leading to enhancement of ethanol-SCR over Ag/Al2O3 by H2. Using VUV-PIMS, the reactive vinyloxy radical was observed in the gas phase during the NOx reduction by ethanol for the first time, particularly in the presence of H2. Identification of such a reaction occurring in the gas phase may be crucial for understanding the reaction pathway of HC-SCR over Ag/Al2O3.

The management of naso-orbital-ethmoid (NOE) fractures.

The bony naso-orbital-ethmoid (NOE) complex is a 3-dimensional delicate anatomic structure. Damages to this region may result in severe facial dysfunction and malformation. The management and optimal surgical treatment strategies of NOE fractures remain controversial. For a patient with NOE trauma, doctors should perform comprehensive clinical examination and radiographic analysis to assess the type and extent of fracture. The results of assessment will assist doctors to make a patientspecific program for the sake of reducing post-operation complications and restoring normal appearance and function as much as possible. This review focuses on the advancement of management of NOE fractures including symptoms, classifications, diagnosis, approaches, treatment and new techniques in this field.