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The tetragonally double alkaline rare earth molybdates NaRe(MoO4)2 (Re = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Er) micro-particles in aqueous solution of Re(NO3)3 and Na2MoO4 were prepared hydrothermally by a facile and effective EDTA-assisted method, and investigated by XRD, SEM, FE-SEM, photoluminescence (PL) excitation and emission spectra. The results showed that the radii of Re ions, pH and the molar ratio of Re(NO3)3/Na2MoO4 in the synthesis solution play an important role in controlling sizes, morphologies and luminescent properties of the final products. And the possible formation mechanism for the bipyramid-like structure and role of EDTA were discussed in detail. The microstructure and PL property of NaYxLa1-x(MoO4)2:10%Eu3+ was investigated, and it showed that NaY0.5La0.5(MoO4)2 exhibited regular sphere-like morphology and emitted the stronger red emission with better color purity than other products. When Tm3+, Dy3+ and Eu3+ with appropriate concentrations were used as dopants to modify this bipyramid NaY(MoO4)2 material, the white light emission material of NaY(MoO4)2:1%Tm3+-11%Dy3+-0.6%Eu3+ was successfully synthesized and its CIE chromaticity coordinates is (0.33, 0.33), which is the standard white light point. These novel white-light-emitting NaY(MoO4)2:1%Tm3+-11%Dy3+-0.6%Eu3+ with single phase would be a promising material in the WLED field. [ABSTRACT FROM AUTHOR]

A series of CuO-ZnO-TiO2 catalysts with various TiO2 loadings were prepared by using a co-precipitation method. The prepared catalysts were characterized by using X-ray diffraction (XRD), N2 adsorption, reactive N2O adsorption, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), hydrogen temperature programmed desorption (H2-TPD), and CO2-TPD techniques, and tested the extent of methanol synthesis from carbon dioxide (CO2) hydrogenation. The results indicate that the addition of TiO2 to the CuO-ZnO catalyst makes the copper species exist in an amorphous-like structure or in much smaller crystallites, which promotes the reduction of CuO. Upon increasing the TiO2 loading, the metallic Cu surface area ( SCu) of the catalyst rises first and then decreases, exhibiting a maximum at a TiO2 loading of 10 %. The results of the catalytic experiments reveal that the addition of TiO2 favors the production of methanol, and an optimum catalytic activity is obtained at a TiO2 loading of 10 %. Moreover, the methanol yield increases linearly with the SCu of the catalysts, thereby indicating that the addition of TiO2 enhances the SCu but not the intrinsic activity. [ABSTRACT FROM AUTHOR]

HZSM-5 zeolites modified with various alkaline earth oxides (MgO, CaO, and BaO) were prepared by using impregnation and mixed physically with Cu/ZnO/Al2O3 to perform the direct synthesis of dimethyl ether (DME) from syngas in a pressurized fixed-bed under continuous flow conditions. The results indicated that the modification effectively enhanced the DME selectivity; MgO and CaO are more effective modifiers than BaO and they improved the DME selectivity up to 67 % as compared to only 54 % over the parent HZSM-5. Moreover, the catalyst prepared from magnesium nitrate exhibits higher DME selectivity than those prepared from magnesium acetate and chloride. The enhancement in the DME selectivity resulted from the effective suppression of hydrocarbon and CO2 formation, which can be attributed to the significant decline in the amount of strong acid sites of the HZSM-5 zeolite resulting from the modification. [ABSTRACT FROM AUTHOR]

A tandem cycle ride: The catalytic reaction mechanism of CO oxidation over Pd‐Cu‐Clx/γ‐Al2O3 is proposed based on DFT studies. There are two catalytic cycles in the CO oxidation process, the palladium cycle (— (green)) and the copper cycle (— (red)). [ABSTRACT FROM AUTHOR]

Ni-modified Ag/SiO2 catalysts containing 0~3 wt.% Ni were obtained by impregnating Ni species onto Ag/SiO2 followed by calcination and reduction. The catalysts' performance in the hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) was tested. Ag-0.5%Ni/SiO2 showed the highest catalytic activity among these catalysts and exhibited excellent catalytic stability. The effects of the Ni content on the structure and surface chemical states of catalysts were investigated by XRF, N2-sorption, XRD, TEM, EDX-mapping, FT-IR, H2-TPR, UV–vis, and XPS. The better catalytic activity and stability of Ni-modified Ag/SiO2 (versus Ag/SiO2) are ascribed to the improved dispersion of active Ag species as well as the higher resistance to the growth of Ag particles due to the presence of Ni species. [ABSTRACT FROM AUTHOR]

Abstract: Rh-Mn-Li catalysts supported on SiO2, ZrO2 and SiO2-ZrO2 mixed oxides with various molar ratios of Si/Zr were prepared and tested for the synthesis of C2-oxygenates from syngas. Compared with pure SiO2 and ZrO2 supported catalysts, catalysts supported on SiO2-ZrO2 mixed oxides showed higher activity and C2-oxygenates selectivity, in which Rh-Mn-Li/SiO2-ZrO2 (molar ratio of Si/Zr=1:3) exhibited the best yield of C2-oxygenates. The effect of the support on the performance of the Rh-based catalysts was investigated comprehensively by XRD, N2 adsorption-desorption, H2 and CO uptakes, FT-IR, XPS, H2-TPR, TPSR and CO-TPD techniques. The results indicated that the chemical state of Rh, CO adsorption species, dispersion of Rh and the ability of CO hydrogenation varied over catalysts supported on SiO2, ZrO2 and SiO2-ZrO2 mixed oxides, which led to the diverse catalytic activity toward C2-oxygenates synthesis. [Copyright &y& Elsevier]

Abstract: A series of Rh–Mn–Li catalysts supported on SiO2 prepared by different methods were tested for the synthesis of C2+ oxygenates via CO hydrogenation. The catalysts were comprehensively characterized by N2 adsorption–desorption, XRD, in situ FT-IR, CO-TPD, TPSR, and H2-TPR. It was found that the Rh–Mn–Li catalyst supported on the SiO2 synthesized by the Stöber method exhibited the highest CO conversion and selectivity toward C2+ oxygenates compared with other catalysts. The investigation based on the catalytic performance and characterizations of the catalysts suggests that the hydroxyl–metal interaction over the catalysts supported on different SiO2 results in different desorption behavior of the adsorbed CO. The specific interaction between the active components and weakly H-bonded hydroxyls on the SiO2 prepared by the Stöber method promoted the transformation from Rh+(CO)2 to Rh–CO and facilitated the desorption/reactivity of adsorbed CO as a function of temperature in the presence of hydrogen, which were proposed to be the crucial factors for obtaining higher CO conversion and C2+ oxygenates selectivity. [Copyright &y& Elsevier]

Abstract: Different amounts of Fe promoted Rh–Mn–Li/SiO2 catalysts were prepared and investigated for the synthesis of C2 oxygenates from syngas. The results showed that the low amount of Fe (≤0.1wt.%) improved the reactivity and yield of C2 + oxygenates, but an opposite effect appeared at high content of Fe (>0.1wt.%). Diffuse reflectance infrared Fourier transform spectroscopy was used to probe the effects of Fe on CO adsorption and hydrogenation, and two opposing effects were evidenced. Moreover, it is proposed that the facile transformation of dicarbonyl Rh+(CO)2 into H–Rh–CO is responsible for high selectivity of C2 + oxygenates. [Copyright &y& Elsevier]

Abstract: A novel SiO2 synthesized by the Stöber method was studied as the support for Rh–Mn–Li catalyst, and better performance for C2 oxygenate synthesis via CO hydrogenation was achieved compared with the counterpart using commercial SiO2 as the support. The investigation based on the catalytic performance and characterizations of the catalysts suggests that the hydroxyl–metal interaction over the catalyst supported on SiO2 prepared by the Stöber method results in a change in the CO adsorption on Rh particles, which promotes the CO dissociation and CO insertion, leading to higher CO conversion and C2 oxygenate selectivity. [Copyright &y& Elsevier]

Abstract: SiO2, TiO2 and SiO2–TiO2 mixed oxide were synthesized by sol–gel method and used as supports for Rh-based catalysts. The effect of support on the performance of Rh-based catalysts for C2-oxygenates synthesis from syngas was investigated by XRD, N2 adsorption-desorption, FT-IR, H2-TPD, H2-TPR and TPSR techniques. The results indicated that SiO2–TiO2 supported catalyst had higher dispersion of Rh and thus more Rh+ sites, better capability for CO adsorption and dissociation, and moderate ability for hydrogenation. As a result, SiO2–TiO2 supported Rh-based catalyst exhibited higher activity and C2 oxygenates selectivity compared with counterparts supported on TiO2 and SiO2. [Copyright &y& Elsevier]

Abstract: A series of Cu/ZrO2 catalysts with various La loadings for methanol synthesis from CO2 hydrogenation were prepared by a urea–nitrate combustion method. The catalysts were characterized with N2 adsorption, XRD, reactive N2O adsorption, XPS, TPR, H2-TPD and CO2-TPD techniques, and tested for methanol synthesis from CO2 hydrogenation. With increasing La loading, the Cu surface area increases first and then decreases, whereas the amount of basic site over catalysts increases continuously. The results of catalytic test reveal that a linear relationship exists between the conversion of CO2 and the Cu surface area. Moreover, it is found for the first time that the selectivity to methanol is related to the distribution of basic site on the catalyst surface. The presence of La favors the production of methanol, and the optimum catalytic activity is obtained when the amount of La doping is 5% of the total amount of Cu2+ and Zr4+. [Copyright &y& Elsevier]

Abstract: A series of HZSM-5 zeolites modified with various contents of antimony oxide (0–30wt.%) were prepared by solid state ion reaction at 500°C, and the acidities of the resulted materials were characterized by temperature-programmed desorption of NH3. The direct synthesis of dimethyl ether (DME) from syngas was carried out over the admixed catalysts of an industrial CuO–ZnO–Al2O3 methanol synthesis catalyst and the parent and antimony oxide modified HZSM-5 zeolites under pressurized fixed-bed continuous flow conditions. The results indicated that modification of HZSM-5 with suitable amount of antimony oxide significantly decreased the selectivity for undesired byproducts like hydrocarbons and carbon dioxide from 9.3% and 32.4% to less than 1% and 28%, respectively, so the selectivity for DME was enhanced greatly from 55% to 69% under temperature of 260°C, pressure of 4MPa and gas hourly space velocity of 1500mLh−1 . The decrease in the formation of hydrocarbons and carbon dioxide can be attributed to the significant decline in the amount of strong acid sites of the HZSM-5 zeolite induced by antimony oxide modification. Additionally, the influences of the operating parameters on the performance of the most efficient catalyst were also investigated. The results showed that high reaction temperature and high gas hourly space velocity resulted in both lower carbon monoxide conversion and lower dimethyl ether selectivity, so they should be no higher than 280°C and 3000mLh−1 , respectively. [Copyright &y& Elsevier]

Abstract: A series of CuO–ZnO–ZrO2 (CZZ) catalysts were synthesized by a glycine–nitrate combustion method and characterized by XRD, BET, N2O chemisorption, SEM and TPR techniques. The results show that the physicochemical properties of the catalysts are strongly influenced by the fuel content used in the combustion process. The dispersion of CuO exhibits an inverse-volcano variation trend with an increase in the glycine amount from 50% to 150% of the stoichiometry. The relationship between physiochemical properties and the fuel content is discussed in detail in terms of combustion temperature. The catalytic performance for the synthesis of methanol from CO2 hydrogenation was examined. The CZZ catalyst exhibits an optimum catalytic activity when 50% of stoichiometric amount of glycine was used. The turnover frequency has been calculated for various CZZ catalysts, and it reveals that the catalytic activities depend not only on the surface area of metallic copper but also on the phase state of ZrO2. [Copyright &y& Elsevier]

Abstract: Various CuO–ZnO–ZrO2 (CZZ) catalysts have been synthesized by urea–nitrate combustion method and their performances for methanol synthesis from CO2 hydrogenation have been investigated. The effects of urea/nitrate ratio on physicochemical and catalytic properties were studied by XRD, BET, H2-TPR and reactive N2O adsorption techniques. The results show that when 50% of stoichiometric amount of urea was used, the CZZ catalyst exhibited an optimum catalytic behavior. The combustion method was found to be a simple, fast and valuable route for the preparation of CZZ catalyst for methanol synthesis from CO2 hydrogenation. [Copyright &y& Elsevier]

Abstract: A series of CuO–TiO2–ZrO2 catalysts with various Ti and Zr molar ratios were prepared by co-precipitation method and characterized by N2 physisorption, X-ray diffraction (XRD) and temperature-programmed reduction of hydrogen (H2-TPR). The prepared CuO–TiO2–ZrO2 samples were mixed physically with HZSM-5 zeolite to synthesize dimethyl ether (DME) via CO2 hydrogenation. The results indicated that CuO–TiO2–ZrO2/HZSM-5 had higher CO2 conversion and DME yield compared to CuO–TiO2/HZSM-5 and CuO–ZrO2/HZSM-5 catalyst, in which the catalyst with equimole of Ti and Zr got the best performance. The activities of CuO–TiO2–ZrO2/HZSM-5 catalysts were well correlated to the reduction properties of CuO–TiO2–ZrO2 samples. [Copyright &y& Elsevier]

Abstract: The effect of B2O3 addition on the crystallization of amorphous TiO2–ZrO2 mixed oxide was investigated by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG/DTA). TiO2–ZrO2 mixed oxide was prepared by co-precipitation method with aqueous ammonia as the precipitation reagent. Boric acid was used as a source of boria, and boria contents varied from 2 to 20wt%. The results indicate that the addition of small amount of boria (<8wt%) hinders the crystallization of amorphous TiO2–ZrO2 into a crystalline ZrTiO4 compound, while a larger amount of boria (⩾8wt%) promotes the crystallization process. FT-IR spectroscopy and 11B MAS NMR results show that tetrahedral borate species predominate at low boria loading, and trigonal borate species increase with increasing boria loading. Thus it is concluded that highly dispersed tetrahedral BO4 units delay, while a build-up of trigonal BO3 promote, the crystallization of amorphous TiO2–ZrO2 to form ZrTiO4 crystals. [Copyright &y& Elsevier]

Abstract: A series of γ-Al2O3 samples modified with various contents of sulfate (0–15wt.%) and calcined at different temperatures (350–750°C) were prepared by an impregnation method and physically admixed with CuO–ZnO–Al2O3 methanol synthesis catalyst to form hybrid catalysts. The direct synthesis of dimethyl ether (DME) from syngas was carried out over the prepared hybrid catalysts under pressurized fixed-bed continuous flow conditions. The results revealed that the catalytic activity of SO4 2−/γ-Al2O3 for methanol dehydration increased significantly when the content of sulfate increased to 10wt.%, resulting in the increase in both DME selectivity and CO conversion. However, when the content of sulfate of SO4 2−/γ-Al2O3 was further increased to 15wt.%, the activity for methanol dehydration was increased, and the selectivity for DME decreased slightly as reflected in the increased formation of byproducts like hydrocarbons and CO2. On the other hand, when the calcination temperature of SO4 2−/γ-Al2O3 increased from 350°C to 550°C, both the CO conversion and the DME selectivity increased gradually, accompanied with the decreased formation of CO2. Nevertheless, a further increase in calcination temperature to 750°C remarkably decreased the catalytic activity of SO4 2−/γ-Al2O3 for methanol dehydration, resulting in the significant decline in both DME selectivity and CO conversion. The hybrid catalyst containing the SO4 2−/γ-Al2O3 with 10wt.% sulfate and calcined at 550°C exhibited the highest selectivity and yield for the synthesis of DME. [Copyright &y& Elsevier]

Abstract: A series of MCM-22 zeolites were prepared by hydrothermal synthesis and subsequent dealumination by oxalic/citric acid leaching and steaming. The structural and acidic properties of the prepared samples were characterized by methods of XRD, ICP-AES, 27Al MAS NMR, pyridine-adsorbed IR and NH3-TPD. The results indicated that the sample treated by oxalic acid (MCM-22O) has the lowest aluminum content while the samples treated by steam have little change of the aluminum content. Unusually, sample MCM-22O possessed the strongest acidity among the dealuminated samples in spite of its lowest content of aluminum. It may be due to its least content of extraframework aluminum, which may lead to the weakening of acidity. Additionally, the prepared zeolites were mixed with a methanol synthesis catalyst and then applied in the process of syngas to dimethyl ether. Citric acid treated sample performed best with the least generation of byproducts, which have been well related to its structural and acidic properties. [Copyright &y& Elsevier]

Abstract: The deactivation and regeneration of B2O3/TiO2-ZrO2 catalyst for the vapor phase Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam were studied. The fresh, deactivated and regenerated catalysts were characterized by using adsorption of nitrogen, X-ray diffraction (XRD), thermogravimetry (TG) and NH3-temperature-programmed desorption (NH3-TPD) techniques. The crystal structure and pore size distribution of the catalyst were retained after reaction, but the number of acid sites decreased significantly. There was a relationship between the amount of coke deposited on the catalyst and the decline in catalytic activity. These results suggest that the coke deposition on the surface of catalyst is mainly responsible for the catalyst deactivation. The catalytic activity can be recovered completely after calcining the deactivated catalyst in air flow at 600°C for 8h. [Copyright &y& Elsevier]

Abstract: A series of HZSM-5 zeolites modified with various contents of magnesium oxide (0–10 wt%) were prepared with an incipient impregnation technique and characterized by X-ray diffraction, N2 adsorption, temperature-programmed desorption of NH3 and CO2, 27Al MAS NMR, and FT-IR. The modified HZSM-5 zeolites were mixed physically with methanol synthesis components (CuO–ZnO–Al2O3) to perform the direct synthesis of dimethyl ether (DME) from syngas under pressurized fixed-bed continuous-flow conditions. The results indicated that modification of HZSM-5 with a suitable amount of MgO significantly decreased the selectivities for undesired by-products like hydrocarbons and CO2 from 9.3 and 37.1% to less than 0.4 and 31%, respectively, through the removal of unselective strong Brønsted acid sites and hence enhanced the selectivity for DME from 49% to more than 64%, whereas the conversion of carbon monoxide was scarcely affected. However, when the MgO contents were equal to or higher than 5 wt%, both the conversion of CO and selectivity for DME decreased markedly because of the decreased activity for methanol dehydration. A mechanism for methanol dehydration to DME involving both acidic and basic sites on the HZSM-5 zeolites modified with MgO has been proposed based on the results obtained. [Copyright &y& Elsevier]

Abstract: The effect of calcination temperature (500–700°C) on the performance of B2O3/TiO2–ZrO2 catalyst for vapor-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam was investigated. Catalysts were characterized by adsorption of nitrogen, X-ray diffraction and ammonia temperature-programmed desorption. The results indicated that the percent of acid sites of medium strength within the total acid sites and the pore size both increased with calcination temperature. Such increases led to increases of the oxime conversion and caprolactam selectivity. However, a large amount of crystalline B2O3 appeared after calcination at 700°C and caused the decrease of the total amount of acid sites, which resulted in remarkable decrease in the activity of the catalyst. Another part of this work focused on the effect of solvent on the catalytic performance of B2O3/TiO2–ZrO2. Solvents with various polarities were investigated for the reaction. It was found that acetonitrile, which has the highest polarity for solvents examined here, was the most effective for the formation of caprolactam. The solvent with high polarity increases the desorption rate of produced caprolactam from catalyst surface, resulting in a high selectivity to caprolactam and low catalyst deactivation rate. FT-IR measurements confirmed the efficient desorption of caprolactam induced by the attack of the acetonitrile molecule. [Copyright &y& Elsevier]

The effects of calcination temperature and preparation method of TiO2–ZrO2 mixed oxide on catalytic performance of B2O3/TiO2–ZrO2 catalysts were investigated. TiO2–ZrO2 mixed oxides with the same molar ratio of 1:1 were prepared by co-precipitation method, homogeneous precipitation method, sol–gel method and physical mixing method; each oxide was calcined at a temperature between 110 and 700 °C. Catalytic synthesis of #x03B5;-caprolactam from cyclohexanone oxime was evaluated in a fixed-bed flow microreactor at 300 °C and atmosphere pressure. Characterization of catalysts was carried out using adsorption of nitrogen, X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR) and temperature-programmed desorption of ammonia (NH3-TPD) techniques. The experimental results reveal that the calcination temperature in the range of 110–500 °C had only a slight effect on the catalytic performance, but after calcination at 700 °C, the ZrTiO4 crystallite was formed and accounted for the decrease of acidity and catalytic performance. The co-precipitation method provided the catalyst with the highest reactivity while the physical mixing method resulted in the worst catalyst. Catalytic performance of the B2O3/TiO2–ZrO2 catalyst was closely related to its acid strength distributions and pore size. [Copyright &y& Elsevier]

Pure TiO2, ZrO2 and TiO2-ZrO2 mixed oxides with various compositions were prepared by the co-precipitation method. Catalysts containing 12 wt.% boria were prepared using these oxides and their catalytic performance for vapor-phase Beckmann rearrangement of cyclohexanone oxime to &epsiv;-caprolactam was determined. With increasing zirconia content in the mixed oxide, the specific surface area and the temperature of the phase transformation increased; maximum values were obtained for a mixed oxide having a Ti and Zr molar ratio of 1/1. XRD results indicated that TiO2-ZrO2 became amorphous after calcination at 500 °C if neither the content of TiO2 nor that of ZrO2 was less than 25%. The yield of lactam increased with increasing zirconia content in mixed oxide and reached a maximum value for the B2O3/TiO2-ZrO2 (1/1) catalyst. With further increase in zirconia content, the lactam yield decreased; the lowest value was observed for the pure ZrO2-supported catalyst. The acidic property and the pore characteristics of the catalyst were key factors that affected its performance. The influences of the operating parameters on the performance of B2O3/TiO2-ZrO2 (1/1) catalyst were also investigated. [Copyright &y& Elsevier]

A novel catalyst, boria supported on titania-zirconia mixed oxide, exhibits very high catalytic activity and selectivity in vapor-phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam. It gives 99.7% oxime conversion and 97.0% lactam selectivity at 300°C. [ABSTRACT FROM AUTHOR]

A series of boria catalysts supported on titania–zirconia mixed oxide (B2O3/TiO2–ZrO2) with different boria loadings (8–20 wt%) were prepared and characterized by X-ray diffraction, adsorption of nitrogen, 11B magic angle spinning (MAS) NMR measurements and temperature-programmed desorption (TPD) of ammonia. The catalytic performance of B2O3/TiO2–ZrO2 for vapor-phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam was studied at 300°C. It was found that the lactam selectivity increased with increasing of boria loading, whereas a maximum oxime conversion was obtained at the boria loading of 12 wt%. The acid sites of medium strength on the surface of the catalyst play an important role in the selective formation of lactam. [ABSTRACT FROM AUTHOR]

H3PW12O40-modified MnOx catalysts (denoted as Mn-HPW) were used for NOx elimination with co-fed NH3. The optimal Mn-HPW0.02 catalyst exhibited over 90% NOx conversion at 90–270 °C. The incorporation of HPW increased the amount of Lewis acid sites of the catalyst for adsorbing NH3, and accelerated the reaction between the adsorbed NH3 species and gas-phase NOx, thus, increasing the low-temperature catalytic activity. The oxidation ability of the Mn catalyst was decreased due to the addition of HPW, thus, mitigating the overoxidation of the adsorbed NH3 species and improving the de-NOx activity and N2 selectivity in the high-temperature region. DRIFT results revealed that the NH3 species on Lewis and Brønsted acid sites, bridged nitrate, and bidentate nitrate were important species/intermediates for the reaction. NH3-SCR over the Mn and Mn-HPW0.02 catalysts obeyed the Eley–Rideal and Langmuir–Hinshelwood mechanisms, simultaneously, at 120 °C. [ABSTRACT FROM AUTHOR]