Search

A series of Cu-ZnO-ZrO2 (CCZ) catalysts were prepared by the solvothermal method with different solvothermal times (1 h, 3 h, 6 h, and 12 h). The physicochemical properties of these catalysts and the catalytic performance for CO2 hydrogenation to methanol were studied. The highest methanol yield was achieved when the solvothermal time was 6 h (CCZ-6). Furthermore, we found that the copper surface area (SCu) increases and then decreases with an increase in the solvothermal time and that there is a strong correlation between the methanol yield and the SCu. This research highlights the crucial influence of the solvothermal time on the structure and catalytic behavior of Cu-ZnO-ZrO2 catalysts, providing a valuable reference for the development of efficient catalysts. [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]

A series of Mn3Co16Ox composite oxides catalysts were fabricated via a solid-phase synthesis using different manganese precursors (namely manganese acetate (A), nitrate (N), and sulfate (S)). It has been demonstrated that the obtained catalysts presented variable catalytic activities for CO oxidation and remarkable diversity of physicochemical properties closely depending on the manganese precursors. In detail, the catalytic activity and catalytic durability for CO oxidation under humid conditions generally followed a descending order of Mn3Co16Ox-A > Mn3Co16Ox-N > Mn3Co16Ox-S. The optimum catalytic performance of Mn3Co16Ox-A was predominantly attributed to its larger specific surface area, significantly higher low-temperature reducibility and lattice oxygen mobility, and more plentiful oxygen vacancies. [ABSTRACT FROM AUTHOR]

UiO-66 and its modified forms (UiO-66-NH2 and UiO-66-OH) were used as supports to prepare Rh–Mn catalysts by using a co-impregnation method, and their catalytic activities were investigated for the direct synthesis of ethanol-based C2+ oxygenates from CO hydrogenation. The catalysts were comprehensively characterized using N2 sorption, XRD, XPS, DRIFT, and TPSR analyses. The structural and textural properties of the catalysts clearly show that Rh and Mn are highly dispersed in the pores of MOFs, but the order of the original structure is partially sacrificed due to the loading of metals and the synergistic effect of Rh, Mn, and Zr would be influenced by various functional groups present in UiO-66. On combining both in situ FT-IR and TPSR analyses, it is confirmed that the higher number of active sites of Rh0 on RM/UiO-66 promotes the CO dissociation ability and hydrogenation rate, which result in its best catalytic activity with the highest yield of C2+ oxygenates, 197.3 g (kg h)−1. [ABSTRACT FROM AUTHOR]

• MCF silica supported CuO CeO 2 catalysts were used for CO oxidation. • CD-assisted co-impregnation was superior to traditional co-impregnation. • Catalyst prepared by CD-assisted method has high activity and stability. • Kind of CD used in preparation has no distinct effect on catalyst activity. • Amount of CD used in preparation has no distinct effect on catalyst activity. A CuO-CeO 2 /MCF catalyst was prepared by cyclodextrin-assisted co-impregnation (CC/M-CD). For comparison, a reference catalyst was prepared by traditional wet impregnation (CC/M). The catalysts were characterized by ICP-OES, XRD, Raman, N 2 -physisorption, TEM, EDS mapping, XPS, in situ DRIFTS, H 2 -TPR, and CO-TPD. The results show that Cu and Ce species of the CC/M-CD catalyst disperse more homogeneously, and the CC/M-CD catalyst has a larger surface area, more amounts of Cu+ and Ce3+ species, enhanced interaction between CuO and CeO 2 , and thus exhibits higher catalytic activity in CO oxidation. Additionally, the kind and amount of cyclodextrin used in the impregnating solutions have no distinct effect on the activity of CC/M-CD prepared by the cyclodextrin-assisted co-impregnation. [ABSTRACT FROM AUTHOR]

A series of fluorinated nano-HZSM-5 zeolite catalysts were prepared by impregnating with NH 4 F solutions of various concentrations and applied to the selective conversion of bio-ethanol to propene at 500 °C, atmospheric pressure, and WHSV of 10 h − 1 . The characterizations by XRD, TEM, N 2 adsorption, ICP-OES, EDX, 27 Al MAS NMR, NH 3 -TPD, Py-IR, and TG techniques revealed that fluoride treatment had a major effect on the channel structure together with the acidic properties. The newly formed mesopores increased the coke tolerance capacity and reduced the probability of coke formation by facilitating mass transfer, and the weakened acidity suppressed the formation of coke. Hence, fluorine modification with suitable content (20 wt%) significantly enhanced the selectivity of propene as well as the catalytic stability. In addition to coke, elimination of aluminum in the zeolite framework was also an important reason for the deactivation of fluorinated nano-HZSM-5 zeolite catalyst. [ABSTRACT FROM AUTHOR]

• CuO-Ce x Zr 1-x O y are prepared via a facile surfactant-assisted grinding method. • CuO-Ce 0.7 Zr 0.3 O y exhibits the highest activity and moisture resistance. • Activity is related to contents of highly dispersed CuO and oxygen vacancies. • CO oxidation catalyzed by CuO-Ce x Zr 1-x O y mainly follows the L-H mechanism. • CuO-Ce 0.7 Zr 0.3 O y exhibits excellent stability and adaptability to space velocity. A series of CuO-Ce x Zr 1-x O y mixed oxides with different Ce contents were prepared via a facile surfactant-assisted grinding method, and their catalytic activity for CO oxidation under dry or moist atmosphere were investigated. The results indicate that the catalyst with a Ce content (x) of 0.7 in Ce x Zr 1-x O y (CuCe 0.7 Zr 0.3) exhibited the best activity under both dry and moist atmospheres, with the temperatures corresponding to CO conversion of 90 % (T 90) at a space velocity of 18000 mL/(g cat · h) being 90 and 120 °C, respectively. Combing with the physicochemical properties of the catalysts obtained by multiple characterization techniques such as ICP-OES, XRD, Raman, N 2 sorption, XPS, in situ DRIFTs, H 2 -TPR, O 2 -TPD and CO-TPD, the high activity of the CuCe 0.7 Zr 0.3 catalyst can be mainly attributed to the existence of large amounts of highly dispersed CuO x species and oxygen defect sites. [ABSTRACT FROM AUTHOR]

• Activation temperature exerts important effect on CuO-CeO 2 catalyst. • The catalyst activated at 550 °C exhibits superior activity and moisture resistance. • Activity is closely related to contents of Cu+ species and oxygen vacancies. • Dispersed CuO with strong interaction with CeO 2 exhibits good moisture resistance. • Bulk CuO with no or weak interaction with CeO 2 exhibits poor moisture resistance. Development of a highly efficient Cu-based catalyst for low-temperature CO oxidation under moisture condition remains a grand challenge. In this paper, effect of activation temperature (350–800 °C) on catalytic performance of CuO-CeO 2 , prepared by facile one-step solvothermal synthesis, in CO oxidation was investigated, and the catalysts' physicochemical properties were studied by TG-DSC, ICP-AES, N 2 sorption, XRD, TEM, Raman spectroscopy, XPS, in-situ DRIFTS, H 2 -TPR, CO-TPD, and O 2 -TPD. It was found that activation at 550 °C is beneficial for the interaction between CuO and CeO 2 , leading to the formation of more Cu+ species and oxygen vacancies advantageous for improving the catalytic activity. Activation at 800 °C, nevertheless, would weaken the interaction between CuO and CeO 2 due to the sintering of CuO and CeO 2 , thus decreasing the catalytic activity and moisture resistance. Interestingly, no deactivation was observed over the optimal catalyst (activated at 550 °C) after 50 h testing at a low temperature of 87 °C (at which 90% CO conversion was obtained), even when 4.2% water vapor was added into the feed gas. [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: 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]

A series of M 3 Co 16 O x (M = Cr, Ti, Zr, Fe, Mn) oxide catalysts wrapped by polymer nanofilm were developed by the solid-phase method, and the catalytic activities were investigated for low temperature oxidation of carbon monoxide under moisture-rich condition. The catalysts were characterized by HR-TEM, FT-IR, XRD, N 2 adsorption-desorption, H 2 -TPR, CO-TPD and XPS techniques. The results reveal that the M 3 Co 16 O x composite oxides are high-dispersive mesoporous materials coated by polymer nanofilm with an average thickness in the scope of 4–7 nm. The percentages of surface oxygen vacancy and lattice oxygen on the catalysts decrease in the following order: Mn 3 Co 16 O x > Fe 3 Co 16 O x > Zr 3 Co 16 O x > Ti 3 Co 16 O x > Cr 3 Co 16 O x , which is consistent with their catalytic performances. Among all the prepared catalysts, the polymer nanofilm wrapped Mn 3 Co 16 O x nanoparticles possess the highest Co 3+ /Co 2+ ratio (1.56), the highest percentage of surface oxygen vacancy (17.5%) and lattice oxygen (62.2%), resulting in the best catalytic activity, such as, 100% conversion at 55 °C under moisture-rich condition (∼0.6 vol.%). Moreover, the Mn 3 Co 16 O x catalyst also exhibits long-term catalytic stability (>one month) even at a very high water vapor level (3.1 vol.%) and considerably low temperature (85 °C). [ABSTRACT FROM AUTHOR]

A series of Cu@ZrO 2 -U framework catalysts derived from Cu@UiO-67 precursors with adjustable copper loadings were constructed by the deposition-precipitation method, and the catalytic activities of methanol synthesis via CO 2 hydrogenation were investigated. The optimized 20-Cu@ZrO 2 -U catalyst showed the best catalytic activity. At 3 MPa and 260 °C, the space-time yield of CH 3 OH (STY CH3OH) reached 2.28 mmol CH3OH /(g cat ·h), which was 3.5 times higher than that of 20-Cu/ZrO 2. The catalyst of 20-Cu@ZrO 2 -U also showed good stability during the 100-h time on stream test. The catalysts were further characterized by XRD, N 2 sorption, TEM, XPS, H 2 -TPR, CO 2 /H 2 -TPD and in situ DRIFTS. The characterization results showed that the stable ZrO 2 framework derived from UiO-67 is propitious to the confine of copper nanoparticles and formation of Cu+-ZrO 2 interfacial sites, which should be responsible for the excellent performance of methanol synthesis. Moreover, in situ DRIFTS was used to probe that the methanol synthesis via CO 2 hydrogenation over 20-Cu@ZrO 2 -U follows a HCOO∗-intermediated reaction pathway. [Display omitted] • A novel Cu@ZrO 2 -U framework catalyst was constructed by Cu@UiO-67 precursor strategy. • The optimized catalyst of 20-Cu@ZrO 2 -U was shown to form rich Cu+-ZrO 2 interfaces. • The methanol yield of 20-Cu@ZrO 2 -U was 3.5 times higher than 20-Cu/ZrO 2 catalyst. • The methanol productivity depends on the ratio of Cu+/Cu0 regulated by Cu+-ZrO 2 interface. • The methanol synthesis mechanism of Cu@ZrO 2 -U follows a HCOO∗-intermediate pathway. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu/ZnO x particles were encapsulated in UiO-66 by deposition–precipitation method. • Both of metal loading and Cu/Zn mole ratio can regulate the Cu-Zn interaction. • The amount of Cu/ZnO x interfaces is related to the methanol synthesis performance. A series of Cu-Zn catalysts encapsulated by Zr-based metal–organic frameworks (UiO-66) with various metal loadings and Cu/Zn mole ratios were prepared by the deposition–precipitation method, and the catalytic activities were investigated by CO 2 hydrogenation to methanol. The results showed that Cu-Zn@UiO-66 catalyst with Cu-Zn loading of 35 wt% and Cu/Zn mole ratio of 2.5 had the best catalytic activity. At 240 °C and 3 MPa, this catalyst gave the excellent catalytic activity with the highest methanol yield of 9.1%, and showed good reaction stability during 100-hour catalytic test. The catalysts were characterized by N 2 -sorption, XRD, TEM, XPS, H 2 -TPR and CO 2 -TPD. Such excellent performance benefits from the ultrasmall nanoparticles (NPs) and abundant Cu/ZnO x interfaces confined in the UiO-66, and the strong interaction between Cu and ZnO promotes the CO 2 conversion and methanol synthesis. [ABSTRACT FROM AUTHOR]

The effect of iron promoter on the catalytic properties of Rh-Mn/UiO-66-drived catalyst was investigated by syngas conversion. The appropriate addition of Fe can enhance the Rh-Fe interaction, resulting in the enhancement of CO dissociation ability and strength of the Rh-CO bond, which should be responsible for the higher CO conversion and selectivity of C 2 + oxygenates. [Display omitted] • Fe-promoted Rh-Mn/UiO-66-drived catalysts were investigated by syngas conversion. • The Rh-Fe interaction can promote the reduction of Rh active sites. • The Rh0-rich state can enhance CO dissociation ability and Rh-CO bond strength. The effect of iron promoter on the catalytic performance of Rh-Mn/UiO-66-drived catalyst was studied by syngas conversion. The catalysts were completely characterized by means of X-ray diffraction (XRD), N 2 sorption, transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), diffuse reflectance infrared Fourier transform spectra (DRIFTS), and temperature-programmed surface reaction (TPSR). When the amount of Fe doping reached 0.3 wt%, the catalyst has the excellent catalytic activity with the highest C 2 + oxygenates yield of 300.1 g/(kg·h). The results indicated that the appropriate addition of iron can enhance the Rh-Fe interaction, which promote the reduction of Rh active sites. The Rh0-rich state would be observed on the catalysts doped by the appropriate amount of Fe, resulting in the enhancement of CO dissociation ability and strength of the Rh-CO bond, which should be responsible for the higher conversion rate and selectivity of C 2 + oxygenates. [ABSTRACT FROM AUTHOR]