查看更多>>摘要：This work is focused on obtaining aromatics from renewable resources by propylene-furan Diels-Alder condensation. Several acid catalysts with different pore topology and SiO2/Al2O3 ratios were considered to gain further understanding of the molecular sieve and acidity effects on the selectivity towards different fractions and the catalytic stability. Experiments were performed in a fixed bed reactor at 500 degrees C, WHSV = 17.4 h(-1) and 3:1 propylene:furan molar ratio. Small pore-size materials (CHA, FER, MOR) are mainly selective to alkenes following cracking and oligomerization pathways, whereas materials with a larger pore size (FAU, MCM-41) produce polycyclic compounds and coke precursors. BEA and mainly MFI zeolites have the optimum topology to produce aromatics, mainly toluene. Experimental results suggest a competition between condensation and alkylation, the first one being promoted by the strongest acidic sites. These data provide the basis of a comprehensive reaction mechanism that allows anticipating the product distribution as a function of the catalytic properties of the considered material.
查看更多>>摘要：The effect of olefin addition to a stream of dimethyl ether on the methanol homologation reaction is investigated using iron-substituted zeolites Fe-beta and Fe-ZSM-5. The reaction was investigated using plug-flow microreactors in the temperature range of 240-400 degrees C, at a total pressure of 0.239 MPa and a WHSV of 6.12 (g DME/ gcat-hr). For Fe-beta (Si/Fe= 9.2) catalysts, isobutene co-feeding almost doubles dimethyl ether (DME) consumption rate and shifts selectivity towards larger olefins with carbon numbers from 5 to 7. Addition of isobutene above 6.3%, however, resulted in a reduction of DME consumption rates, an effect assigned to the replacement of surface methoxy groups for adsorbed olefins in the zeolite pores. Below a temperature of 340 degrees C hydride-transfer rates are negligible; reaction rates are stable for over 5.5 h and the products consist almost exclusively of olefins and a small amount of methane. Above 360 degrees C the onset of catalytic hydride transfer processes is observed leading to fast catalyst deactivation rates and an increase in the concentration of aromatic species. Iron ZSM-5 (Si/Fe = 21.4) catalysts under similar reaction conditions consumes methanol faster than Febeta at approximately three times the TOF (on a per iron basis). The Fe-ZSM-5 catalyst was selective to a distribution of products (C5 to C8) as compared to Fe-beta which was selective to primarily C5 and C7. Co-feeding larger olefins (2-methyl-2-butene, 2,3-dimethyl-2-butene, 2,3,3-trimethyl-1-butene, and 2,4,4-trimethyl-2-pentene) at a 3.9% olefin concentration over Fe-beta changed selectivity towards cracking products (C4 compounds such as isobutene). As the size of the olefin increases, a reduction of DME consumption rate is also observed. These results show that co-feeding olefins with DME over Fe-zeolites is a promising route to increase methylation rates at relatively low temperatures producing larger branched olefins and that the product distribution is highly dependent on the zeolite pore size and structure of the olefin.
Ha, SuKee, Benjamin L.Wang, Wei-JyunAkpolat, Osman...
7页
查看更多>>摘要：The Caustic Aqueous Phase Electrochemical Reforming (CAPER) process can convert aqueous-phase ethanol to high-pressure and high-purity hydrogen (H-2) at lower cell operating temperatures and voltages than traditional methods. Additionally, any carbon dioxide (CO2) produced by the ethanol electrochemical oxidation is captured by the caustic electrolyte solution. Without using a membrane, the only gas-phase species is H-2. The CAPER process achieves process intensification for compressed and pure H-2 production by eliminating the need for downstream separation and external compression steps. All the compression is performed on the liquid-phase reactants to circumvent less efficient gas-phase compression. This study uses a high-pressure batch electrochemical reactor to demonstrate the capability of the CAPER reforming process and investigates catalytic behavior under operating conditions. Our Tafel analysis showed that both palladium and platinum nanoparticles on carbon supports have high activity for ethanol electro-oxidation under the caustic electrolyte condition (exchange current density (i(0)) > 1 x 10(-5) A cm(-2)), while non-noble nanoparticles on carbon supports showed poor activity. The only gas phase product was pressurized H-2 and its faraday efficiency was determined as 100%. The exchange current density was not affected by high-pressure operation. The carbon selectivity toward unwanted byproduct acetate on the anode increased from 17% to 63% as the applied anode potential increased from -500 mV to -200 mV vs. Ag/AgCl.
查看更多>>摘要：Herein, a new axial g-C3N4 coordinated iron(III) phthalocyanine (FeP/CN) was fabricated for peroxymonosulfate (PMS) activation. Around 100% degradation of acetaminophen (AP), 2,4-dichlorophenol (2,4-DP), sulfadiazine (SDZ), and methyl orange (MO) (30 mg L-1) were achieved within 20 min by adding 0.02 g L-1 FeP/CN5 (3.62 wt % Fe) and 0.2 mM PMS. High-valent iron-oxo species (FeIV=O) was demonstrated as the main reactive species, which mediated a two-electron transfer process with pollutants. Characterizations and computational analysis revealed that the axial g-C3N4 ligand provided Fe(III) coordination environments to generate FeIV=O species directly through PMS activation, and increased the reactivity of the FeIV=O species in pollutants oxidation due to the narrowed HOMO-LUMO gap. Besides, small displacement of Fe atom (0.23 A) from the macrocycles plane due to the axial g-C3N4 ligand decreased the iron demetalization rate from 3.54% to 0.28% in the catalyst/PMS system. This work offered an excellent strategy to design high-efficiency catalysts for FeIV=O generation.
查看更多>>摘要：New insights into reaction mechanism for catalytic methane combustion are provided in broad operating conditions on Pd/La0.7MnO3 as model natural gas vehicle catalyst. Under lean and dry conditions, a dual mechanism is suggested with active sites combining reactive oxygen species from La0.7MnO3 and palladium instead of single site reaction mechanism. Aging in wet atmosphere has no consequence on the kinetic behavior. On the other hand, in wet atmosphere near the stoichiometry, strong accumulation of hydroxyl groups on the support would suppress the metal-support interface. Accordingly, methane combustion would take place only on Pd particles.
查看更多>>摘要：Zn-Al mixed oxides with different acidic and basic natures were synthesized under different pH (8.0-9.5) conditions and applied to the amination of methanol (MeOH). The physical and chemical properties of the samples were characterized using X-ray diffraction (XRD), N-2 sorption, and X-ray photoelectron spectroscopy (XPS), as well as temperature-programmed desorption (TPD) with different probe molecules, such as NH3, CO2, iso-propanol (IPA), and MeOH. The conversion of MeOH and selectivity to acetonitrile (ACN) increased as the pH of the synthetic mixture increased to 9.5. The activity of the catalysts was in good accordance with the desorption temperatures of propylene in IPA-TPD and dimethyl ether in MeOH-TPD, while their selectivity to ACN was well correlated with the proportion of the weak base sites on the surface of the catalyst. Particularly, the changes in the acidity and basicity of the catalysts with the synthesis pH were mainly influenced by the degree of disorder of the ZnAl2O4 spinel structure. During the amination of MeOH, the catalytic activity, product selectivity, and deactivation behavior of the catalysts were affected by the reaction parameters. The Zn-Al mixed oxide catalyst was readily regenerated by via simple calcination, which removed the carbonitride and coke that were formed during the reaction.
Bobadilla, L. F.Centeno, M. A.Odriozola, J. A.Martinez T, L. M....
12页
查看更多>>摘要：The aim of this work was to clarify the effect of the support on CO selective methanation with Ru/TiO2 catalysts. TPR, XRD and TEM measurements confirmed that the changes in the activity and selectivity should be ascribed to anatase:rutile ratio, RuO2 +TiO2 solid solution formation, as well as the metal content and the thermal treatment used. All these characteristics result in active and selective catalysts in which the suppression of the reverse water gas shift reaction was observed. The catalytic performance must be explained by both the formation of more active Ru species as a result of support influence and the higher Ru dispersion. The study allows to conclude that for CO activation the role of support surface hydroxyls seems to be determinant for both the activity and selectivity of Ru/TiO2 catalysts.
查看更多>>摘要：In this work, 2 wt%Pt/TiO2, 20 wt%Ni/TiO2 monometallic catalysts and xwt%Pt-20 wt%Ni/TiO2 (x = 1, 2 and 4 wt%) bimetallic catalysts were synthesized by one-pot sol-gel method for CO2 methanation reaction. All bimetallic catalysts revealed higher CO2 conversion than both monometallic catalysts. The 2 wt%Pt-20 wt%Ni/TiO2 catalyst exhibited the highest percentage of CO2 conversion at low reaction temperature, with almost 100% CH4 selectivity and high stability during 72 h time on stream. The effect of Pt co-doped with Ni to bimetallic formed on the catalyst properties was studied using several techniques, including X-ray diffraction, N-2 adsorption-desorption, Raman spectroscopy, transmission electron microscopy, field emission scanning electron microscopy, H-2 temperature-programmed desorption, H-2 temperature-programmed reduction, CO2 temperature-programmed desorption and X-ray absorption spectroscopy (both ex-situ and in-situ experiments). The results showed that Pt was dispersed on the catalyst surface in the form of platinum oxide, while Ni was both incorporated into the TiO2 lattice with the excess amount from saturated level being dispersed on the catalyst surface. The results from XAS evidenced that some electrons movement from Ni to Pt occurred. This electronic property changing can tune the interaction between Ni and TiO2 support with appropriate strength and then resulting in higher reducibility of the catalyst and higher dispersion of Ni species. Furthermore, the electron-rich Pt site on the catalyst surface favored to adsorb CO from CO2 dissociation and further activated adsorbed CO to interact with nearby hydrogen atoms to form CH4 leading to high CO2 methanation activity at low temperature.
NSTL
Elsevier