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1.
The K2CO3/MoS2 catalyst for higher alcohols synthesis with synthesis gas as feedstock was prepared. The catalyst was characterized by TPR, in-situ XPS, XRD and SEM. Effects of pretreatment with H2, CO or synthesis gas on activity and selectivity of the catalyst were investigated. Results showed that there was a remarkable induction period about 180 h at the initial reaction stage for the un-treated catalyst. The catalytic performances for alcohols synthesis changed notably during the induction period. The induction period was confirmed to be resulted primarily from the sulfur losing and K element dispersion on the surface of ADM catalysts. Pretreatment of the catalyst could remarkably shorten the time of induction period as well as promote the catalytic activity. Furthermore, the higher alcohols (C2 + OH) content in the liquid products were enhanced after the catalyst pretreated by CO or synthesis gas which could be ascribed to the increasing of Mo4+ content on the surface of the catalyst. 相似文献
2.
The effect of the addition of CeO2 to Pt/C catalysts on electrochemical oxidation of alcohols (methanol, ethanol, glycerol, ethylene glycol) was studied in alkaline solution. The ratios of Pt to CeO2 in the catalysts were optimised to give the better performance. The electrochemical measurements revealed that the addition of CeO2 into Pt-CeO2/C catalysts could significantly improve the electrode performance for alcohols oxidation, in terms of the reaction activity and the poisoning resistance, due to the synergistic effect. The electrode with the weight ratio of Pt to CeO2 equals 1.3:1 with platinum loading of 0.30 mg/cm2 showed the highest catalytic activity for oxidation of ethanol, glycerol and ethylene glycol. 相似文献
3.
Formation of H2O2 from H2 and O2 and decomposition/hydrogenation of H2O2 have been studied in aqueous acidic medium over Pd/SiO2 catalyst in presence of different halide ions (viz. F−, Cl− and Br−). The halide ions were introduced in the catalytic system via incorporating them in the catalyst or by adding into the reaction medium. The nature of the halide ions present in the catalytic system showed profound influence on the H2O2 formation selectivity in the H2 to H2O2 oxidation over the catalyst. The H2O2 destruction via catalytic decomposition and by hydrogenation (in presence of hydrogen) was also found to be strongly dependent upon the nature of the halide ions present in the catalytic system. Among the different halides, Br− was found to selectivity promote the conversion of H2 to H2O2 by significantly reducing the H2O2 decomposition and hydrogenation over the catalyst. The other halides, on the other hand, showed a negative influence on the H2O2 formation by promoting the H2 combustion to water and/or by increasing the rate of decomposition/hydrogenation of H2O2 over the catalyst. An optimum concentration of Br− ions in the reaction medium or in the catalyst was found to be crucial for obtaining the higher H2O2 yield in the direct synthesis. 相似文献
4.
The Fe2O3/Al2O3 catalyst was studied to selectively synthesize mixed alcohols from syngas in a continuously stirred slurry reactor with the oxygenated solvent Polyethylene Glycol-400 (PEG-400). The selectivity of mixed alcohols in the products reached as high as 95 wt.% and the C2+ alcohols (mainly ethanol) was more than 40 wt.% in the total alcohol products at the reaction conditions of 250 °C, 3.0 MPa, H2/CO = 2 and space velocity = 360 ml/gcat h. The hydrogen temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) measurements of the catalyst confirmed that the FeO phase was responsible for the high selectivity to mixed alcohols in the process. And the oxygenated solvent PEG-400 was also necessary for the selective synthesis of mixed alcohols in the reaction system. 相似文献
5.
The effects of adding mixtures of titania and zirconia on the methanol synthesis activity and selectivity of Cu/SiO2 were investigated. The synthesis of methanol from both CO/H2 and CO2/H2 mixtures was examined at 0.65 MPa and temperatures between 448 and 573 K. For CO hydrogenation, the addition of ZrO2 alone increased the methanol synthesis activity of Cu/SiO2 by up to three-fold. Substitution of a portion of the ZrO2 by TiO2 decreased the methanol synthesis activity of the catalyst relative to that observed when only ZrO2 is added. ZrO2 addition also enhanced the methane synthesis activity by as much as seven fold. In the case of CO2 hydrogenation, the maximum methanol synthesis activity is achieved when a 50/50 wt% mixture of ZrO2 and TiO2 is added to Cu/SiO2. Neither the presence of the oxide additive nor its composition had any effect on the activity of the reverse water–gas-shift reaction, which suggests that this reaction proceeds only on Cu. The observed effects of ZrO2 and TiO2 on the catalytic activity of methanol synthesis from CO and CO2, and methane synthesis from CO, are interpreted in terms of the strength and concentration of acidic and basic groups on the surface of the dispersed oxide. 相似文献
6.
Xiaomin Yang Xiuna Wang Changhai Liang Weiguang Su Chuang Wang Zhaochi Feng Can Li Jieshan Qiu 《Catalysis communications》2008,9(13):2278-2281
The unique and significant promotion effect of water has been evidenced by the selective oxidation of benzyl alcohol to benzaldehyde over Au/TiO2 catalysts. Water has dual promotional functions in the reaction system: to help form unique microdroplets in a multiphase reaction system and to assist the oxygen adsorption and activation. The conversion of benzyl alcohol at a molar ratio of water to solvent (p-xylene) of 7 is 7 times higher than in the absence of water. The present work has highlighted the potential of Au/TiO2 catalysts in aerobic oxidation of alcohols in the unique multiphase reaction system with water as promoting solvent. 相似文献
7.
D. Martín Alonso R. Mariscal R. Moreno-Tost M.D. Zafra Poves M. Lpez Granados 《Catalysis communications》2007,8(12):2074-2080
A K/γ-Al2O3 catalyst was prepared using the wet impregnation method with K2CO3 as a precursor salt. During the activation process, a clear interaction between potassium carbonate-derived species and the support took place resulting in the formation of K aluminate-like species, as observed by evolved gas analysis by mass spectrometry (EGA-MS) and infrared spectroscopy (FTIR). This catalyst was tested in the transesterification of sunflower oil with methanol, achieving a methyl ester yield close to 100% after 1 h. However, when it was used in successive runs the catalyst showed a strong decrease in its catalytic performance. It is established experimentally that the performance in the first run was mainly due to a homogeneous contribution from active basic species dissolved in methanol. The leaching of potassium species in the reaction media was not avoided although a clear interaction between active phase and support was observed. The present work stresses the obligation of the reutilization and of the verification of the leaching of active species in analogous catalytic systems based on alkaline and alkaline-earth metal oxides when used in the transesterification reaction with methanol. 相似文献
8.
Congwei Wang Na Liu Liwei Pan Sheng Wang Zhongshan Yuan Shudong Wang 《Fuel Processing Technology》2007
Oxidative steam reforming of methanol (OSRM) reaction was investigated over a novel monolithic ZnO–Cr2O3/CeO2–ZrO2 catalyst developed in our laboratory. A novel flat-bed reactor was designed to measure the concentration profiles of the monolithic catalyst beds under different operation conditions: water-to-methanol mole ratio (W/M) between 1 and 1.5; oxygen-to-methanol mole ratio (O/M) in the range of 0.1–0.3; space velocity ranging from 1840 to 2890 h− 1; and reaction temperature in the scale of 400–440 °C. On the basis of these results, reaction pathways for the OSRM were discussed. It is indicated that only three independent reactions dominate in our reaction system, namely, the partial oxidation of methanol, the steam reforming of methanol and the methanol decomposition reaction, whereas the water–gas shift and the reverse water–gas shift reactions should be ignored. In addition, the steam reforming of methanol proceeds along all the catalyst bed, whereas methanol decomposition and oxidation reactions occur mainly at the entrance of the catalyst bed. 相似文献
9.
The possibility of electrochemically promoting the water–gas-shift reaction and the CO oxidation reaction in a PEM fuel cell reactor supplied with a methanol reformate mixture was investigated in PEM fuel cells with Pt or Au state-of-the-art E-TEK anodes, in order to explore the use of PEMFC units as preferential oxidation of CO (PROX) reactors. The electropromotion of CO removal was investigated both with air or H2 fed to the cathode side and also by O2 bleeding to the anode during normal PEMFC operation. It was found that the catalytic activity of the anode for CO conversion to CO2 can be modified significantly by varying the catalyst potential. The magnitude of the electrochemical promotion depends strongly on the anodic electrocatalyst (Pt or Au), on the CO concentration of the fuel mixture, on the operating temperature and on the presence of oxygen. The electropromotion effect and the Faradaic efficiency were found to be much higher in CO-rich anode environments. 相似文献
10.
Copper(I) chloride catalysts with a loading of 20 wt%, supported on silica–titania mixed oxides with Si/Ti ratios of 1, 5, 10 and 50 were prepared by conventional and microwave heating methods and tested in the oxidative carbonylation of methanol to dimethyl carbonate (DMC). X-ray diffraction (XRD), nitrogen adsorption, X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis (TGA) were used to examine the bulk and surface properties of the CuCl/SiO2–TiO2 catalysts. Quantum-chemical calculations were performed to explore the interaction of CuCl with the silica–titania support. Microwave heating showed some significant advantages over the conventional heating method, with markedly reduced preparation temperature and time, and provided improved catalytic activity in the oxidative carbonylation of methanol. The catalytic behavior of CuCl/SiO2–TiO2 in the test reaction studied was strongly dependent on the support composition. Incorporation of tetrahedral Ti(IV) species into the silica matrix could enhance the interaction of copper species with the oxide support. The improved catalytic performance of CuCl/SiO2–TiO2 in the DMC synthesis can be understood by the existence of the strong coordination interactions between the Cu+ centers of CuCl and the bridging oxygen atoms at the Si–O–Ti bonds in the silica–titania support. 相似文献
11.
This study investigates the use of CaO-CeO2 mixed oxides as solid base catalysts for the transesterification of Pistacia chinensis oil with methanol to produce biodiesel. These CaO-CeO2 mixed-oxide catalysts were prepared by an incipient wetness impregnation method and characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The cerium improved the heterogeneous catalytic stability remarkably due to the defects induced by the substitution of Ca ions for Ce ions on the surface. The best catalyst was determined to be C0.15-973 (with a Ce/Ca molar ratio of 0.15 and having been calcined at 973 K), considering its catalytic and anti-leaching abilities. The effects of reaction parameters such as the methanol/oil molar ratio, the amount of catalyst amount and the reaction temperature were also investigated. For the C0.15-973 regenerated after five reuses, the biodiesel yield was 91%, which is slightly less than that of the fresh sample. The test results revealed that the CaO-CeO2 mixed oxides have good potential for use in the large-scale biodiesel production. 相似文献
12.
Xiaoming Guo Dongsen Mao Guanzhong Lu Song Wang Guisheng Wu 《Catalysis communications》2011,12(12):1095-1098
Cu/ZnO/ZrO2 catalysts were prepared by a route of solid-state reaction and tested for the synthesis of methanol from CO2 hydrogenation. The effects of calcination temperature on the physicochemical properties of as-prepared catalysts were investigated by N2 adsorption, XRD, TEM, N2O titration and H2-TPR techniques. The results show that the dispersion of copper species decreases with the increase in calcination temperature. Meanwhile, the phase transformation of zirconia from tetragonal to monoclinic was observed. The highest activity was achieved over the catalyst calcined at 400 °C. This method is a promising alternative for the preparation of highly efficient Cu/ZnO/ZrO2 catalysts. 相似文献
13.
Cu/ZnO/Al2O3 catalysts with Cu/Zn/Al ratios of 6/3/1 were precipitated and aged by conventional and microwave heating methods and tested
in the slurry phase reactor for methanol synthesis. The effect of technological condition of precipitation and aging process
under microwave irradiation on the catalytic performance was investigated to optimize the preparing condition of Cu/ZnO/Al2O3 catalyst. The results showed that the microwave irradiation during precipitation process could improve the activity of the
catalyst, but had little effect on the stability. While the microwave irradiation during aging process has a great benefit
to both the activity and stability of the catalyst, the catalyst aged at 80°C for 1 h under microwave irradiation possessed
higher methanol space time yield (STY) and more stable catalytic activity. The activity and stability of the catalyst was
further enhanced when microwave irradiation was used in both precipitation and aging processes; the optimized condition for
the catalyst precursor preparation was precipitation at 60°C and aging at 80°C under microwave irradiation. 相似文献
14.
Juan Fernández Jessely Molina Tamara Rajmankina José Arévalo álvaro Parada 《Polymer Bulletin》2007,59(5):629-636
Summary (C5H5)2Zr(O2C)CH3 and (C5H5)2Zr(O2C)CH2CH3 complexes were synthesized, characterized and activated with MAO for ethylene polymerization. The highest catalytic activity
was achieved at Al/Zr molar ratio of 3000 for both systems. The effects of the size of the R group in the carboxylate ligands,
the Al/Zr molar ratio and reaction temperature on the catalytic activity and polymer properties were studied and discussed. 相似文献
15.
Xiao-Long Yang Wei-Qiang Zhang Chun-Gu Xia Xu-Mao Xiong Xin-Yuan Mu Bin Hu 《Catalysis communications》2010,11(10):867-870
The nanocrystalline barium cerate (BaCeO3) was synthesized and examined as a support promoting ammonia synthesis catalyzed by particulate Ru. It was quite worthy noting that Ru/BaCeO3 catalyst exhibited superior activity to the conventional ruthenium catalysts supported on γ–Al2O3, MgO and CeO2 at low reaction temperature. The characterization including XRD, HRTEM, XPS and TPR results demonstrated that electronic interaction between Ce (IV) and Ru metals combined with strong metal-support interaction was responsible for such high catalytic activity at low reaction temperature. 相似文献
16.
Selective oxidation of methanol to dimethoxymethane (DMM) was conducted in a fixed-bed reactor over an acid-modified V2O5/TiO2 catalyst. The influence of the acid modification on its structure, redox and acidic properties, and catalytic performance for methanol oxidation were investigated. The results indicated that the content of vanadia in the catalyst exhibits a vital influence on the dispersion of vanadium species, while the acid modification can enhance its surface acidity. Proper amounts of the acid (W() = 15%) and V2O5 (W(V2O5) = 15%) components loaded in the acid-modified V2O5/TiO2 catalyst are able to build a bi-functional circumstance that is favorable for the formation of DMM with high activity and selectivity. As a result, for the selective oxidation of methanol, the H2SO4-modified V2O5/TiO2 catalyst gives a much higher DMM yield at 150 °C than the unmodified one. 相似文献
17.
D. Reichert T. Finke N. Atanassova H. Bockhorn S. Kureti 《Applied catalysis. B, Environmental》2008,84(3-4):803-812
This study deals with the catalytic reaction of NOx and soot on Fe2O3 to yield N2 and CO2 in excess of oxygen. Based on the three types of kinetic experiments, i.e. temperature programmed oxidation (TPO), transient examinations and gradient-free loop reactor experiments, as well as mechanistic studies presented recently a global kinetic model is established. The model includes catalytic effect of the iron oxide on soot/O2 reaction, whereas it is assumed that NOx reduction occurs on the soot without direct participation of Fe2O3. Furthermore, the model implies global kinetic expressions for the COx formation and NOx reduction. These equations include the evolution of the surface area of soot and the correlation of reactive carbon sites (Cf) with those specifically involved in NOx reduction (C*). The kinetic model is sequentially developed by accounting for the catalytic and non-catalytic soot/O2 as well as soot/NOx/O2 conversion. Kinetic parameters are taken from the literature and are also determined from a fit to experimental data. Comparison of measured and calculated data shows accurate reproduction of the experiments and the model. Finally, the kinetic model is validated by some simulations. 相似文献
18.
S?awomir Ku? 《Fuel》2003,82(11):1331-1338
The catalytic performance in oxidative coupling of methane (OCM) of unmodified pure La2O3, Nd2O3, ZrO2 and Nb2O5 has been investigated under various conditions. The results confirmed that the activity of La2O3 and Nd2O3 was always much higher than that of the remaining two. The surface basicity/base strength distribution of pure La2O3, Nd2O3, ZrO2 and Nb2O5 was measured using a test reaction of transformation of 2-butanol and a temperature-programmed desorption of CO2. Both methods showed that La2O3 and Nd2O3 had high basicity and contained medium and strong basic sites (lanthanum oxide more and neodymium oxide somewhat less). ZrO2 had only negligible amount of weak basic sites and Nb2O5 was rather acidic. The confrontation of the basicity and catalytic performance indicated that in the case of investigated oxides, the basicity (especially strong basic sites) could be a decisive factor in determination of the catalytic activity in OCM. Only in the case of ZrO2 it was observed a moderate catalytic performance in spite of negligible basicity. The influence of a gas atmosphere used in the calcination of oxides (flowing oxygen, helium and nitrogen) on their basicity and catalytic activity in OCM had been also investigated. Contrary to earlier observations with MgO, no effect of calcination atmosphere on the catalytic performance of investigated oxides in OCM and on their basicity was observed. 相似文献
19.
《Journal of Catalysis》1999,181(2):271-279
The catalytic activity of Cu(100) and Ni/Cu(100) with respect to the methanol synthesis from various mixtures containing CO2, CO, and H2have been studied in a combined UHV/high pressure cell apparatus at reaction conditions,Ptot=1.5 bar andT=543 K. For the clean Cu(100) surface it is found that admission of CO to a reaction mixture containing CO2and H2does not lead to an increase in the rate of methanol formation, which indirectly suggests that the role of CO in the industrial methanol process relates to the change in reduction potential of the synthesis gas. For the Ni/Cu(100) surface it is found that Ni does not promote the rate of methanol formation from mixtures containing CO2and H2. In opposition, admission of CO to the reaction mixture leads to a significant increase in the rate of methanol formation with a turnover frequency/Ni site∼60×the turnover frequency/Cu site at Ni coverages below 0.1 ML making it a rather substantial promoting effect. It is found that the admission of CO to the synthesis gas creates segregation of Ni to the surface, whereas this is not the case for a reaction involving CO2and H2. It is suggested that CO acts strictly as a promotor in the system and we ascribe the increase in activity to a promotion through gas phase induced surface segregation of Ni. 相似文献
20.
A catalyst containing gold nanoparticles with Pt/α-Fe2O3/C was prepared by a co-precipitation method and its catalytic activity for the oxidation of methanol, formaldehyde, and formic acid in alkaline solutions was evaluated by an electrochemical method and high-performance liquid chromatography (HPLC). The addition of gold nanoparticles improved catalytic activity only for the oxidation of methanol and formaldehyde, and not for the oxidation of formic acid. HPLC analysis was performed for methanol oxidation to detect the oxidative products. In HPLC analysis, only formate anion could be detected in the electrolyte solution and the ratio of formate anion obtained to the total passed charge in Pt/nano-Au/α-Fe2O3/C was less than that in Pt/C, indicating that formic acid is not the final product of methanol oxidation. These results show that gold nanoparticles promoted methanol oxidation up to CO2. 相似文献