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1.
The nanocatalysts of VOx deposited on ZrO2 supports with single monoclinic (ZrO2-M), tetragonal (ZrO2-T), and binary monoclinic-tetragonal (ZrO2-MT) phase were synthesized. VOx/ZrO2-MT catalysts exhibit better performance during propane nonoxidative dehydrogenation than VOx/ZrO2-M and VOx/ZrO2-T catalysts. Among VOx/ZrO2-MT catalysts, the conversion and deactivation rate constant of VOx/ZrO2-M31T69 catalyst is 35.2% and 0.22 h−1, respectively. The promoting role of ZrO2-MT is revealed by experiments and theoretical calculations. The MT-mixed phase structure in VOx/ZrO2-MT catalyst improves the structural properties and dispersion of VOx. The tetragonal-monoclinic transformation on the ZrO2-MT surface facilitates VOx reduction and produces additional V3+ active sites. The highly dispersed V3+ sites on the ZrO2-MT surface accelerate C H bond breaking and boost the desorption of propylene, which is the key reason for enhancing activity and stability during the reaction, respectively. Insight into the role of surface phase transformation of ZrO2-MT is expected to obtain high-efficient catalysts further.  相似文献   

2.
Ketonization of valeric acid, which can be obtained by lignocellulosic biomass conversion, was carried out in a fixed bed flow reactor over ZrO2, 5–20 % CeO2/ZrO2 and CeO2 both under hydrogen and nitrogen stream at 628 K and atmospheric pressure. Regardless gas-carrier 10 wt% CeO2/ZrO2 was found to show higher catalytic activity compared to zirconia per se as well as other ceria modified zirconia while ceria per se exhibited very low catalytic activity. All catalysts provided higher acid conversion in H2 than in N2 whereas selectivity to 5-nonanone was insensitive to gas atmosphere. XRD, FTIR, UV–Vis DRS, XPS, HRTEM methods were applied to characterize catalysts in reduced and unreduced states simulating corresponding reaction conditions during acid ketonization. XRD did not reveal any changes in zirconia and ceria/zirconia lattice parameters as well as crystalline phase depending on gas atmosphere while insertion of ceria in zirconia caused notable increase in lattice parameter indicating some distortion of crystalline structure. According to XPS, FTIR and UV–Vis methods, the carrier gas was found to affect catalyst surface composition leading to alteration in Lewis acid sites ratio. Appearance of Zr3+ cations was observed on the ZrO2 surface after hydrogen pretreatment whereas only Zr4+ cations were determined using nitrogen as a gas-carrier. These changes of catalyst’s surface cation composition affected corresponding activity in ketonization probably being crucial for reaction mechanism involving metal cations catalytic centers for acid adsorption and COO? stabilization at the initial step.  相似文献   

3.
In this article, two acid catalysts (ZrO2/SO42? and HZSM‐5) and two base catalysts (MgO/MCM‐41 and KtB) were used in catalytic hydrothermal liquefaction (HTL) of Dunaliella tertiolecta (D. tertiolecta) for the production of bio‐oil. The results indicated that the acid/base property of the catalyst plays a crucial role in the catalytic HTL process, and the base catalyst is conducive to the improvement of conversion and bio‐oil yield. When KtB was used as the catalyst, the maximum conversion and bio‐oil yield was 94.84 and 49.09 wt %, respectively. The detailed compositional analysis of the bio‐oil was performed using thermogravimetric analysis, elemental analysis, FT‐IR, and GC‐MS. The compositional analysis results showed that the introduction of catalyst is beneficial for reducing the fixed carbon content in the bio‐oil, and the structure of catalyst influences on the bio‐oil composition and boiling point distribution. Based on our results and previous studies, the probable catalytic HTL microalgae model over various catalysts can be described that the main chemical reactions include ketonization, decarboxylic, dehydration, ammonolysis, and so forth. with HZSM‐5 and MgO/MCM‐41 as the catalyst; the cyclodimerization, decomposition, Maillard reaction, and ketonization are the main reactions with ZrO2/SO42? as the catalyst; the dehydration, ammonolysis, Maillard reaction, and ketonization can occur with KtB as the catalyst. Therefore, a plausible reaction mechanism of the main chemical component in D. tertiolecta is proposed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1118–1128, 2015  相似文献   

4.
Supported VOx catalysts are promising nonoxidative propane dehydrogenation (PDH) materials for their commercially attractive activity and propylene selectivity. However, they frequently suffer from rapid deactivation caused by coke deposition. This article describes the promoting role of magnesium on the stability of VOx/Al2O3 catalysts for PDH. A series of VOx/Al2O3 and Mg‐modified VOx/Al2O3 catalysts were synthesized by an incipient wetness impregnation method. The catalysts were carefully characterized by Raman spectra, UV‐Vis spectra, STEM, TGA and in situ DRIFTS. We showed that the stability of a 12V/Al2O3 catalyst was significantly improved on addition of small amounts of MgO. Experimental evidences indicate that V2O5 nanoparticles emerge in the 12V/Al2O3 samples, and appropriate Mg addition helps dispersing the V2O5 nanoparticles into 2D VOx species thus decreasing coke formation and improving stability in nonoxidative dehydrogenation of propane. © 2017 American Institute of Chemical Engineers AIChE J, 2017  相似文献   

5.
A comparison study was performed of the water-gas shift (WGS) reaction over Pt and ceria-promoted Pt catalysts supported on CeO2, ZrO2, and TiO2 under rather severe reaction conditions: 6.7 mol% CO, 6.7 mol% CO2, and 33.2 mol% H2O in H2. Several techniques—CO chemisorption, temperature-programmed reduction (TPR), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES)—were employed to characterize the catalysts. The WGS reaction rate increased with increasing amount of chemisorbed CO over Pt/ZrO2, Pt/TiO2, and Pt-CeO x /ZrO2, whereas no such correlation was found over Pt/CeO2, Pt-CeO x /CeO2, and Pt-CeO x /TiO2. For these catalysts in the absence of any impurities such as Na+, the WGS activity increased with increasing surface area of the support, showed a maximum value, and then decreased as the surface area of the support was further increased. An adverse effect of Na+ on the amount of chemisorbed CO and the WGS activity was observed over Pt/CeO2. Pt-CeO x /TiO2 (51) showed the highest WGS activity among the tested supported Pt and Pt-CeOx catalysts. The close contact between Pt and the support or between Pt and CeO x , as monitored by H2-TPR, is closely related to the WGS activity. The catalytic stability at 583K improved with increasing surface area of the support over the CeO2- and ZrO2-supported Pt and Pt-CeO x catalysts.  相似文献   

6.
Novel catalysts, SnxZr1-xO2 solid solutions, for NO selective catalytic reduction:NO SCR) are reported. They have much higher activity and selectivity than SnO2 and ZrO2. Sn4+ is the main reductive sites as proved by TPR. The dilution of Sn sites by the coexisting Zr causes a suppression of propene combustion and consequently promoted the selective reduction of NO. The rutile structure might be beneficial to NO SCR.  相似文献   

7.
A series of active oxygen material CexZr1?xO2‐supported Ni? Co bimetallic nanosized catalysts were prepared by coprecipitation method, which is simple and fit for industrial use with lower cost than other methods. The effect of CeO2/ZrO2 mole ratio, Co metal addition, and PEG‐6000 addition were investigated. The catalysts were characterized through X‐ray diffraction, H2 thermal‐programmed reduction, N2 adsorption, Raman spectroscopy, CO pulse chemisorption, X‐ray photoelectron spectroscopy, oxygen storage capacity, and transmission electron microscopy‐energy dispersive X‐ray analysis. Modifications of the structural and redox properties of these materials were evaluated in relation to their catalytic performances. Particularly, the relationship between the active oxygen sites of the catalysts and their catalytic performances was investigated. The interaction between active metals (Ni and Co) and CexZr1?xO2 support was found to be very important for catalytic performance. The active oxygen site of CexZr1?xO2 can considerably improve catalytic performance. Appropriate Co metal addition also remarkably enhanced the catalytic stability and activity. Moreover, PEG‐6000 addition can improve the Brunauer–Emmett–Teller surface area and active metal dispersion of catalysts to improve their performances. The nanosized catalyst 15 wt % Ni‐5 wt % Co/Ce0.25Zr0.75O2 prepared by adding 5 wt % PEG‐6000 achieved almost 85% CO2 conversion and 98% selectivity to methane at 280°C when the gas hourly space velocity was 10,000 h?1. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2567–2576, 2013  相似文献   

8.
The catalytic behavior of ZrO2 and ZrO2 containing 8 mol‐% Y2O3 supported A1–xSrxMnO3 (A = La, didymium) perovskites was studied in the total oxidation of methane, chloromethane and dichloromethane considering catalyst deactivation and byproduct formation. The perovskites are dispersed on the support surface; clusters with a perovskite‐like structure were formed. The supported catalysts are characterized by higher specific surface areas compared with the unsupported ones. Partial substitution of A‐site cations by Sr leads to an enhancement of the catalytic activity in the total oxidation of methane, but not in the total oxidation of chlorinated hydrocarbons (CHC). The catalytic activity of supported and unsupported catalysts is comparable in the total oxidation of methane in spite of the significantly lower perovskite content of the supported catalysts. In the CHC conversion the catalytic activity of the supported catalysts is higher than that of the unsupported ones.  相似文献   

9.
《Ceramics International》2020,46(4):4394-4401
MnOx-CeO2 (denoted as Mn–Ce) nanorod and MnOx-CeO2 nanooctahedra catalysts were synthesized by the hydrothermal method and were used for selective catalytic reduction of NO with NH3. The catalytic performance tests showed that the NO removal efficiency of CeO2 catalysts was obviously improved after loading MnOx. The structure and properties of catalysts had been characterized by SEM、TEM、XRD、BET、XPS、H2-TPR、NH3-TPD and in situ DRIFTS. It was found that Mn–Ce catalyst were of uniform core-shell structure, higher concentrations of Mn4+ and Ce3+, better reducibility, the increase of weak acid sites. The results of in situ DRIFTS indicated that the NH3-SCR reaction should obey the E–R mechanism. Moreover, the promotion effect and mechanism of MnOx doped CeO2 was demonstrated, which improved the catalytic activity of Mn–Ce catalysts.  相似文献   

10.
Mn/Al2O3 and Mn/ZrO2 were prepared by precipitation method. Their catalytic activity was investigated in the synthesis of biologically important bis(indolyl)methanes via, a condensation reaction between an indole and different aldehydes. The materials exhibited excellent catalytic activity (TOF in the range 180–380 h?1) and produced the expected product in good yield and selectivity. Isolation of product from the reaction mixture was simple and neat. The catalysts were found to be recyclable and used up to five cycles without any loss in their catalytic activity. Mn/ZrO2 was also found to be a better catalyst than Mn/Al2O3 in terms of isolated yield of the product and recyclability. Mn/ZrO2 catalyst was found to be selective for aldehydes and not for ketones. In order to investigate the relationship between the catalytic activity and physico-chemical properties, Mn/Al2O3 and Mn/ZrO2 were characterized for their surface and bulk properties by PXRD, BET, TPD-NH3 and SEM techniques. A good correlation between the catalytic activity of the materials and the concentration of the acid sites with intermediate strength was observed. Mn/ZrO2 exhibited rod like structure. This material was found to be a general catalyst for the synthesis of a number of bis(indolyl)methane derivatives with good yield and selectivity.  相似文献   

11.
BACKGROUND: The catalytic degradation of aqueous Fischer–Tropsch (FT) effluents to fuel gas over Ru/AC has been investigated. In order to understand the catalytic performance and stability of oxide‐supported Ru catalysts, several oxide supports (titania, zirconia, γ‐alumina and silica) were selected for study, with a focus on the hydrothermal stability of catalysts. RESULTS: The catalytic efficiency for transforming the oxygenates in aqueous FT effluents to C1–C6 alkanes decreased in the order: Ru/ZrO2~ Ru/TiO2 > Ru/SiO2 > Ru/Al2O3. The conversion of alcohols was greatly suppressed over Ru/γ‐Al2O3. The former two catalysts (Ru/ZrO2 and Ru/TiO2) exhibited enhanced efficiency and long‐term stability (400 h) relative to Ru/SiO2 and Ru/Al2O3. N2‐physisorption, XRD and SEM showed that titania and zirconia exhibited high structural stability in an aqueous environment. However, the structures of γ‐alumina and silica were unstable due to significant drop in surface area and adverse changes in surface morphology. Especially for the case of the Ru/γ‐Al2O3 catalyst, the γ‐alumina was transformed into boehmite structure after reaction, and metal leaching and carbon deposition were extensive. CONCLUSION: Ru/ZrO2 or Ru/TiO2 may be a promising alternative for degrading aqueous FT effluents due to their long‐term stability. Copyright © 2012 Society of Chemical Industry  相似文献   

12.
The selective oxidation of methane with molecular oxygen over MoOx/La–Co–O and MoOx/ZrO2 catalysts to methanol/formaldehyde has been investigated in a specially designed high-pressure continuous-flow reactor. The properties of the catalysts, such as crystal phase, structure, reducibility, ion oxidation state, surface composition and the specific surface area have been characterized with the use of XRD, LRS, TPR, XPS and BET methods. MoOx/La–Co–O catalysts showed high selectivity to methanol formation while MoOx/ZrO2 revealed the property for the formation of formaldehyde in the selective oxidation of methane. 7 wt MoOx/La–Co–O catalyst gave 6.7 methanol yield (ca. 60 methanol selectivity) at 420°C and 4.2 MPa. On the other hand, the maximal yield of formaldehyde ca. 4 (47.8 formaldehyde selectivity) was obtained over 12wt MoOx/ZrO2 catalyst at 400 °C and 5.0MPa. 7MoOx/La–Co–O catalyst showed higher modified H2-consumption than 12MoOx/ZrO2 catalyst. The reducibility and the O/O2– ratio of the catalysts may play important roles on the catalytic performance. The proper reducibility and the O/O2– ratio enhanced the production of methanol in selective oxidation of methane. [MoO4]2– species in MoOx/ZrO2 catalysts enable selective oxidation of methane to formaldehyde.  相似文献   

13.
The catalytic activities of Cu/MOx (MOx = Al2O3, TiO2, and ZnO) catalysts in the gas‐phase hydrogenolysis of glycerol were studied at 180–300 °C under 0.1 MPa of H2. Cu/MOx (MOx = Al2O3, TiO2, and ZnO) catalysts were prepared by the incipient wetness impregnation method. After reduction, CuO species were converted to metallic copper (Cu0). Cu/Al2O3 catalysts with high acidity, high specific surface areas and small metallic copper size favored the formation of 1,2‐propanediol with a maximum selectivity of 87.9 % at complete conversion of glycerol and a low reaction temperature of 180 °C, and favored the formation of ethylene glycol and monohydric alcohols at high reaction temperature of 300 °C. Cu/TiO2 and Cu/ZnO catalysts exhibited high catalytic activity toward the formation of hydroxyacetone with a selectivity of approx. 90 % in a wide range of reaction temperature.  相似文献   

14.

Abstract  

Co/ZrO x /SiO2 catalysts with enhanced dispersion of Co0 and turnover frequency were successfully prepared combining two different promotion effects, i.e., modifications of SiO2 surface with ZrO x by liquid phase deposition and influencing coordination structure of Co species using chelating agents or glycols. The catalysts exhibited ~6.3-fold higher CO conversion than Co/SiO2 and those promoted by organic additives or ZrO x alone, indicating activity enhancement was induced by cooperation of these two promoters.  相似文献   

15.
Rare earth metal (Ce, La, or Pr) doped Mn-based catalysts were prepared to obtain amorphous Mn–Ce–Ox, Mn–La–Ox and Mn–Pr–Ox. Promotional effects of NO conversion at low temperature were observed after rare earth metal doping. The Mn–Ce–Ox catalyst had the best oxidation performance and the maximum NO oxidation conversion was 94.0% at the reaction temperature of 239 °C. Among the reported Mn-based catalysts for NO oxidation, the Mn–Ce–Ox catalyst showed superior low-temperature activity. The SEM, XRD, BET and XPS analyses further confirmed that the amorphous structure of the catalyst contributed a lot to the enhancement of activity.  相似文献   

16.
X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses have been used to characterize the structure of a La2O3-promoted MnOx/SiO2 catalyst, before and after its utilization in the oxidative dehydrogenation of ethylbenzene (EB). MnOx/SiO2 and MnOx/La2O3/SiO2 catalysts were prepared by pore volume impregnation, using aqueous solutions of (i) La3+-nitrate at an atomic ratio of La/Si = 0.08, and (ii) Mn2+-nitrate at an atomic ratio of Mn/Si = 0.10, followed by drying and calcination at 500°C in air. XRD data show no diffraction patterns specific to MnOx on the La2O3-promoted MnOx/SiO2 catalyst, after calcination. Thus, the presence of La2O3 apparently favors the dispersion of manganese oxides during calcination, presumably by forming mixed Mn-La oxides. On the fresh promoted and unpromoted catalysts, after calcination, XRD and XPS analyses indicated that Mn was present mostly as MnO2 and Mn2O3. In the used catalyst, Mn from the unpromoted catalyst degenerated from Mn4+ to Mn2+, resulting in formation of Mn3O4 species, whereas in the case of La2O3-promoted catalyst Mn remained well dispersed as MnO2 and Mn2O3. It appears that La2O3 precludes the formation of Mn3O4 during the EB dehydrogenation, conserving Mn structure and oxidation state. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

17.
In this paper a detailed study of the (ZrO2)1‐x(Y2O3)x (x=0.025–0.15), (ZrO2)1‐x(Sc2O3)x (x = 0.06 – 0.11) and (ZrO2)1‐x‐y(Sc2O3)x(Y2O3)y (x=0.07 – 0.11; y=0.01 – 0.04) solid solution crystals grown by skull melting technique is presented. The structure, phase composition, and ion conductivity of the obtained crystals were investigated by X‐ray diffraction, transmission electron microscopy, Raman scattering spectroscopy, and impedance spectroscopy. Maximum conductivity as (ZrO2)1‐x(Y2O3)x and (ZrO2)1‐x(Sc2O3)x solid solution crystals is observed for the compositions containing 10 mol% stabilizing oxide, and the conductivity of 10ScSZ is ~3 times higher than for 10YSZ. Experiments on crystal growth (ZrO2)1‐xy(Sc2O3)x(Y2O3)y solid solutions showed that uniform, transparent crystals 7Sc3YSZ, 7Sc4YSZ, 8Sc2YSZ, 8Sc3YSZ, 9Sc2YSZ, 9Sc3YSZ, 10Sc1YSZ, and 10Sc2YSZ are single phase crystal containing t″ phase. It is established that a necessary condition of melt growth of (ZrO2)1‐xy(Sc2O3)x(Y2O3)y single‐phase crystals is the total concentration of the stabilizing oxides from 10 to 12 mol%. The addition of Y2O3 affects the (ZrO2)1‐xy(Sc2O3)x(Y2O3)y solid solution conductivity different ways and depends on the Sc2O3 content in the starting composition. The effects of structure, phase composition, concentration, and type of stabilizing oxides on the electrical characteristics of obtained crystals are discussed.  相似文献   

18.
The NO reduction by ethanol over barium promoted Pd/ZrO2 catalyst and the effect of the oxygen on the selectivity were studied. The catalysts were prepared by incipient wetness impregnation with 14.3% of Ba over zirconia and 1% of palladium. The specific surface areas were 58 and 47 m2/g and the dispersions of Pd were 37% and 30% for the Pd/ZrO2 and Pd–Ba/ZrO2 catalysts, respectively. The X-ray diffraction patterns indicate the presence of monoclinic zirconia phase on the support and BaCO3, which is decomposed at 715 and 815 °C. Temperature programmed desorption profiles of NO on Pd/ZrO2 and Pd–Ba/ZrO2 catalyst showed a huge amount N2 formation for the promoted Ba catalyst. Catalytic results showed high NO conversion even at low temperature, in accordance with the TPD results and an increasing selectivity to N2 when compared with Pd/ZrO2. The effect of O2 in the NOx reduction with ethanol provoked less NO dissociation and lower selectivity to methane.  相似文献   

19.
The Ce modified In/W–ZrO2 catalysts were prepared by impregnation and mechanical mix method. Their activities for SCR of NO x with methane were investigated. The activity of the In/W–ZrO2 catalyst was enhanced by addition of Ce with both methods, while the promotional effect was more pronounced for catalyst prepared by mechanical mix method compared to impregnation method. The function of Ce was to improve the oxidation of NO to NO2. The maximum NO x conversion over the mechanical mixed catalyst can be stabilized at 74% at 450 °C in a dry gas flow and 37% at 500 °C in wet flow (24,000 h−1). For the impregnated catalysts, Ce was found to compete with In to adsorb on strong acid site over W–ZrO2 support and inhibited the formation of InO+, which resulted in the lower activity of these catalysts than mechanical mixed catalysts.  相似文献   

20.
《Ceramics International》2022,48(18):25772-25780
In an attempt to enhance the sintering and mechanical performance of porous cordierite ceramics (Mg2Al4Si5O18) as support materials for vehicle exhaust catalysts, ZrO2 and MxOy (M = La, Ce, and Nb) were simultaneously introduced into cordierite sintered at 1350 °C for 4 h. Then, the reinforced function of ZrO2 and MxOy on the properties of porous cordierite ceramics was systematically evaluated, especially for the sample co-doped with ZrO2 and La2O3. The results displayed a distinct enhancement in mechanical and thermal performance, and the cold compressive strength increased from 72.74 to 158.59 MPa as well as thermal conductivity ranged from 1.66 to 2.01 W m?1 K?1, respectively. It is found that ZrO2 facilitated activation sintering introduced via lattice distortion in cordierite and La2O3 accelerated the formation of cordierite and ZrSiO4 microcrystalline through the low-temperature liquid phase. The synergic effect between ZrO2 and La2O3, therefore, had a significant role in the reinforced mechanical and thermal performance of porous cordierite ceramics. This work not only offers a feasible strengthening strategy, but also expands the possibilities for building high-performance structural and functional ceramics.  相似文献   

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