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Pd/Al

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 NH

The study was conducted to develop a visual and intuitive quantitative evaluation method for maxillary cystic lesions after curettage. Mimics 16.0 and Geomagic Studio 2013 were used to form a precise reconstruction of the cystic lesion morphology of 60 cases; the average reduction rates and 95% confidence interval were calculated. Computed tomography (CT) registration was performed before and after surgery to observe morphology features of the bone regeneration of the cystic area. The average reduction rates (RR) of the cysts after curettage were (43.56 ± 16.79)%, (54.33 ± 17.15)% and (68.53 ± 15.99)% at 3 months, 6 months and 12 months after surgery, respectively. The average monthly reduction rates (MRR) were (12.07 ± 4.35)%, (8.16 ± 2.84)% and (5.35 ± 1.52)% at 3 months, 6 months and 12 months after surgery, respectively. Correlation analysis by comparing with each group showed that the effect of sex and age in the 3-month group and the initial size in the 12-month group on RR and MRR were statistically significant. Within the limitations of the study it seems that the chosen approach for quantitative evaluation of the therapeutic effect of curettage for jaw cystic lesions might facilitate visual and quantitative follow-up of cyst curettage and timely detection of recurrence.

Selective catalytic reduction of NO

Alumina supported Pd catalyst (Pd/Al2O3) is active for complete oxidation of methane, while often suffers transient deactivation during the cold down process. Herein, heating and cooling cycle tests between 200 and 900°C and isothermal experiments at 650°C were conducted to investigate the influence of NOx on transient deactivation of Pd/θ-Al2O3 catalyst during the methane oxidation. It was found that the co-fed of NO alleviated transient deactivation in the cooling ramp from 800 to 500°C, which was resulted from the in situ formation of NO2 during the process of methane oxidation. Over the Pd/θ-Al2O3, thermogravimetric analysis and O2 temperature programmed oxidation measurements confirmed that transient deactivation was due to the decomposition of PdO particles and the hysteresis of Pd reoxidation, while the metal Pd entities were less active for methane oxidation than the PdO ones. CO pulse chemisorption and scanning transmission electron microscopy characterizations rule out the NO2 effect on Pd size change. Powder X-ray diffraction and X-ray photoelectron spectroscopy characterizations were used to obtain palladium status of Pd/θ-Al2O3 before and after reactions, indicating that in lean conditions at 650°C, the presence of NO2 increases the content of active PdO on the catalyst surface, thus benefits methane oxidation. Homogeneous reaction between CH4, O2, and NOx may be partially responsible for the alleviation above 650°C. The interesting research of alleviation in transient deactivation by NOx, the components co-existing in exhausts, are of great significance for the application.

A combined study on the anti-sintering ability, SO2-poisoning mechanism and thermal regeneration property of CeWSnOx catalysts for NH3-SCR reaction.

For NOx control in the presence of excess oxygen, selective catalytic reduction with ammonia (NH3-SCR) has been successfully applied in the purification of coal-fired flue gas and diesel vehicle exhaust on a large scale. For both cases, various NH3-SCR catalysts have been developed, with the incorporation of desirable catalytic properties being the central issue. However, the fundamental principle for designing NH3-SCR catalysts with high activity, selectivity, and stability remain unclear. Generally, in the NH3-SCR reaction, the redox and acid sites on the catalyst are prerequisites that need to work together. Therefore, the close coupling of these dual functional sites is imperative for the design of NH3-SCR catalysts with high NOx removal efficiency. Taking this intrinsic principle into account, we successfully designed and developed various novel catalysts with excellent NH3-SCR performance. This review will focus on the theory and practice of designing metal oxide catalysts for NH3-SCR.

Vanadia-based catalysts have been widely used for catalyzing various reactions, including their long-standing application in the deNOx process. It has been commonly considered that various vanadium species dispersed on supports with a large surface area act as the catalytically active sites. However, the role of crystalline V2O5 in selective catalytic reduction of NOx with NH3 (NH3-SCR) remains unclear. In this study, a catalyst with low vanadia loading was synthesized, in which crystalline V2O5 was deposited on a TiO2 support that had been pretreated at a high temperature. Surprisingly, the catalyst, which had a large amount of crystalline V2O5, showed excellent low-temperature NH3-SCR activity. For the first time, crystalline V2O5 on low-vanadium-loading catalysts was found to be transformed to polymeric vanadyl species by the adsorption of NH3. The generated active polymeric vanadyl species played a crucial role in NH3-SCR, leading to remarkably enhanced catalytic performance at low temperatures. This new finding provides a fundamental understanding of the metal oxide-catalyzed chemical reaction and has important implications for the development and commercial applications of NH3-SCR catalysts.

We analyzed the supply and demand for tilapia in China while assessing the future developmental trends. China has become the world’s largest producer, exporter, and consumer of tilapia. China entered a period of rapid aquaculture development in the 1990s, and the tilapia supply has increased yearly. Tilapia products are mainly supplied to the international market, especially the US. The global market for the Chinese tilapia has grown dramatically, but a downward trend occurred in 2019–2020. The Chinese domestic market demand is relatively stable, and even the COVID-19 epidemic did not significantly impact the supply and demand of tilapia. Internationally, it is expected that the demand for tilapia will decline considerably in the near future. However, this decline could be alleviated after the impact of the COVID-19 epidemic passes and increasing demand will resume. The increased supply of Chinese tilapia might slow down or even decrease due to market uncertainty, the increasing constraints on natural resources, and the Chinese government’s requirements for high-quality aquaculture environments.

Ammonia leakage from the aftertreatment of diesel vehicles arouses serious environmental concerns, thus demanding a high-efficiency ammonia elimination catalyst. In the present work, the mechanism ...

Mn-based oxides exhibit outstanding low-temperature activity for the selective catalytic reduction of NOx with NH3 (NH3-SCR) compared with other catalysts. However, the underlying principle responsible for the excellent low-temperature activity is not yet clear. Here, the atomic-level mechanism and activity-limiting factor in the NH3-SCR process over Mn-, Fe-, and Ce-based oxide catalysts are elucidated by a combination of first-principles calculations and experimental measurements. We found that the superior oxidative dehydrogenation performance toward NH3 of Mn-based catalysts reduces the energy barriers for the activation of NH3 and the formation of the key intermediate NH2NO, which is the rate-determining step in NH3-SCR over these oxide catalysts. The findings of this study advance the understanding of the working principle of Mn-based SCR catalysts and provide a fundamental basis for the development of future generation SCR catalysts with excellent low-temperature activity.

The role of silver species in the H2-assisted NH3 selective catalytic reduction of NOx (H2-NH3-SCR) over Ag/Al2O3 catalysts was investigated by operando spectroscopy (DRIFTS-MS and DR-UV–Vis) and Density Functional Theory (DFT) calculation. UV–Vis analysis showed that several kinds of silver species were present on the Ag/Al2O3, including dispersed silver cations, partially oxidized silver clusters, metallic silver clusters, and silver nanoparticles. Operando DRIFTS-MS experiments showed that the reduction of NOx was dependent on the formation rate of nitrates, which was closely related to the silver content, H2 concentration, and reaction temperature. Notably, operando DR-UV–Vis experiments unambiguously confirmed that the metallic silver clusters were the active sites for nitrates formation, and the reduction of silver nitrates was much slower than NO oxidation. DFT calculations further revealed that reducing silver nitrates required higher energy barriers than NO oxidation, while H2 dissociation could occur on metallic silver clusters with a moderate energy barrier. In conclusion, metallic silver clusters contributed to the formation of nitrates and H2 dissociation, and the reduction of silver nitrates was the rate-determining step in the overall H2-NH3-SCR reaction.

The control of soot emission from diesel vehicles is of extraordinary importance to the environment, and catalytic removal of soot is a highly effective and clean method. Here, we report a novel, non-noble metal catalyst for application in the catalytic combustion of soot with superb activity and resistance to H2O and SO2. MnOx oxide was prepared via a hydrothermal method, and then, Cs and Co were loaded on MnOx by impregnation. The 5%Cs/1%Co/MnOx catalyst displayed excellent catalytic activity with values of T10 (332 °C), T50 (371 °C), and T90 (415 °C) under loose contact. The as-prepared catalysts were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), H2 temperature-programmed reduction (TPR), O2 temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS). The results suggest that, after the introduction of Cs and Co into the MnOx oxide, more NO2 molecules take part in soot oxidation, exhibiting higher NO2 utilization efficiency; this is due to the synergistic effects of multiple components (Cs, Co, and Mn) promoting the generation of more surface-active oxygen and then accelerating the reaction between NO2 and soot. This study provides significant insights into the development of high-efficiency catalysts for soot oxidation, and the developed 5%Cs/1%Co/MnOx catalyst is a promising candidate for application in diesel particulate filters.

Ag/Al2O3 catalysts containing different precipitable silver compounds (AgCl, Ag2SO4, and Ag3PO4) were synthesized and investigated for NOx reduction in H2-assisted C3H6-selective catalytic reduction (SCR). The samples were systematically characterized by N2 adsorption, X-ray diffraction (XRD), UV–Vis, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM). N2 adsorption revealed that the introduction of anions (Cl–, SO42–, and PO43–) did not significantly affect the surface and structural properties of the Al2O3 support. However, XRD patterns and HR-TEM images indicated that the addition of Cl– anions caused the agglomeration of silver species to form large AgCl particles on the AgCl/Al2O3 catalysts. In contrast, the silver species dispersed well on Ag2SO4/Al2O3 and Ag3PO4/Al2O3 catalysts. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed that partial oxidation of C3H6 on Ag2SO4/Al2O3 produced large amounts of reactive enolic species, while it tended to yield inert formate on AgCl/Al2O3. As a result, Ag2SO4/Al2O3 catalysts, especially 3% Ag2SO4/Al2O3, exhibited superior water and sulfur tolerance in H2-assisted C3H6-SCR.