查看更多>>摘要：Lead salts poisoning was a great challenge for the catalysts application in selective catalytic reduction(SCR)reaction of NOx with NH3 in stationary sources.Herein,several typical transition metal(Cu,Co and Zr)oxides modified Mn-Ce/AC catalysts were prepared by impregnation method,and the effects of Cu,Co and Zr doping on resistance PbCl2 poisoning for the catalyst were investigated.The addition of three transition metal oxides improved the PbCl2 resistance of Mn-Ce/AC catalyst and maintained excellent low-temperature denitrification activity of the catalyst.The lead resistance performance of the three metal oxides followed:Cu>Co>Zr oxides.The NO conversion of Cu-doping catalyst after PbCl2 poisoning was only ca.10% lower than that of fresh Mn-Ce/AC catalyst at 225 ℃.Cu,Co and Zr doping could decrease the loss of specific surface area caused by poisoning,while Cu-doped catalyst showed lowest crystallinity of active components.Meanwhile,the contents of Mn~(4+)and chemisorbed oxygen in Cu-doped catalyst were higher than those in Co-or Zr-doped catalysts.Cu,Co and Zr doping improved the surface acidity and redox performance of the poisoned catalysts,with Cu-doped poisoned catalyst exhibiting nearly the same surface acidity and redox performance as the fresh Mn-Ce/AC catalyst.Furthermore,Cu doping could also improve NO adsorption and was in favor to the SCR process.Besides,in situ DRIFTS results showed that the catalytic reaction pathways of all the poisoned or modified catalysts were in accordance with both Langmuir-Hinshelwood(L-H)and Eley-Rideal(E-R)mechanisms.Finally,a possible anti-PbCl2 poisoning mechanistic model of(Cu,Co and Zr)oxides modified on Mn-Ce/AC catalyst was proposed.
查看更多>>摘要：A novel explosion-assistant strategy was developed to fabricate graphene oxide supported nickel and palladium three-component catalyst Pd/Ni/NiO/GO for hydrogenation of nitriles to secondary amines.The explosion during the synthesis of catalyst was essential to the well-dispersion of palladium and the decomposition of metal salt precursors.Palladium component was well anchored on nickel oxide and graphene oxide sheets,which regulated the catalytic performance of palladium.This special structure facilitated the spillover of active hydrogen species generated on palladium component to nickel(oxide)and graphene oxide sheets,enhancing the catalytic activity of the bimetallic catalyst.This work developed an effective strategy to fabricate multi-component metal catalyst with low-cost ttansition metal as main composition for selective hydrogenation of nitriles to secondary amines.
查看更多>>摘要：In the present work,in-depth characterization techniques combined with kinetic analyses were used to develop a deep understanding of the remarkable catalytic performance observed during propane dehydrogenation(PDH)over Ge-promoted Pt/SiO2.Following our previous work on Pt-Ge/Al2O3,we found Ge to significantly affect Pt catalytic performance,reaction mechanism and kinetics,regardless of the nature of the support.The synthesized catalysts were characterized using XAS,XPS,TPR,TGA,C3H6/C3H8-TPD,HRTEM,CO-chemisorption,BET,and CO-DRIFT.Upon Ge promotion to Pt nanoparticles supported on a large,neutral,SiO2 surface area,the bimetallic samples showed higher activation energy,lower desorption energy of C3H6,lower coke formation rates,and higher CsH6 selectivity as compared to the results from using the unpromoted catalyst.Ruling out the neutral SiO2's support effect,the kinetic study indicates the C3H8 reaction order remains close to 1 for all the samples,while the H2 reaction order decreases from 0.04 to-0.52 with increasing Ge loading from 0 wt% to 5 wt%.According to the kinetic analysis,the first C-H bond cleavage seems to be the rate-determining step.The addition of Ge enhances the adsorption of hydrogen,which explains the change of the hydrogen reaction order and the apparent activation energy exhibited by the bimetallic samples.
查看更多>>摘要：Metal-dopant modification is a promising approach to enhance the catalytic performance of titanium silicate molecular sieve.Herein,titanium silicalite-1(TS-1)with different titanium contents and a series of metal-doping modified TS-1 are prepared,to enhance the synthesis of ethylene glycol(EG)through oxidative hydration of ethylene.The EG selectivity show a volcano relationship along with the increase of Ni addition,and reach maximum in 80.63 % at 0.13 wt % Ni loading.The Ni promoter mechanism is revealed that NiO species enhances the electropositivity of skeleton Ti and neutralizes the surface acidity of TS-1,which improves the efficient utilization of H2O2 and selectivity of EG.Furthermore,Ni-modified TS-1 shows superior stability to TS-1,as well as satisfactory reusability since the deactivation of catalyst is reversible through high-temperature calcination.This work demonstrates the feasibility and mechanism of Ni promoter and provides a promising strategy for the development of TS-1 catalysts.
查看更多>>摘要：The temperature effect on propane dehydroaromatization pathways on the PtZn/SiO2 +ZSM-5 bifunctional catalysts is investigated to develop strategies for propane conversion to valuable liquid hydrocarbons.At high temperature(550 ℃),high dehydrogenation rates and lower monomolecular cracking rates are required to minimize methane formation,leading to primarily propene and BTX(benzene,toluene,and xylenes).By recycling propene in the propane conversion range of 30-45%,>80% BTX yields is likely achievable at full recycle.At mid temperature(400-450 ℃),the product has high selectivity to gasoline-blending hydrocarbons(butanes,C_5~+ hydrocarbons,toluene,and xylenes)at 15-25% propane conversions because dehydrogenation rates are moderately high,and oligomerization is more favored than cracking.At low temperature(350 ℃),~25% propane conversion is achieved and has high selectivity(~60%)to butanes,but the propane conversion rates are likely too low to be practical.While methane formation by monomolecular cracking limits liquid yields at high reaction temperature,hydrogen co-produced at high propane conversions saturates light olefins to make un-desired ethane,which becomes major yield loss reaction on the PtZn/SiO2 +ZSM-5 at mid and low temperatures.
查看更多>>摘要：A novel MnOx catalyst(Mn-MP)derived from MOF-Mn3(BTC)2(H2O)6 was fabricated and investigated for the selective catalytic reduction of NOx by NH3 at low temperatures.Mn-MP catalyst showed a superior activity and noticeably improved tolerance to SO2.The MOF precursor and doping PVP led to large surface area,small particle size and more crystalline defects of Mn-MP catalyst.The formation of abundant acid sites,Mn~(4+)and surface chemical oxygen would promote the NH3-SCR reaction.In situ DRIFTs demonstrated the high SO2 tolerance over the Mn-MP catalyst not only results from the reduced irreversible sulfurization rate,but also the promoting adsorption of active bidentate nitrates and NH4 in the coexistence of sulfates.Our work shed light on the design of porous MOF-derived MnOx catalysts with high SO2 resistance at low temperatures.
查看更多>>摘要：Stable Pd nanoparticles(Pd NPs)have been uniformly dispersed and immobilized into the metal-organic framework of UiO-66,Pd/UiO-66,by a facile impregnation reduction method.Pd/UiO-66 retains the integrity of the UiO-66 crystal structure and incorporated with ultrasmall Pd NPs(1.70 ± 0.32 nm).Using ammonium formate(AF)as a H-donor and water as solvent under green condition,the optimized 1.16 wt% Pd/UiO-66 catalyst exhibits remarkable activity in the catalytic transfer hydrogenation(CTH)of a-mefhylstyrene(AMS)into cumin(achieving 99.6% conversion of AMS and almost full selectivity to cumin with an extremely high turnover frequency value 456.7 h~(-1)at 323.15 K).Pd/UiO-66 also show superior catalytic activity in CTH of unsaturated alkene compounds to saturated compounds with excellent stability and recyclability.Furthermore,the as-formed saturated alkanes can be fast and automatic separated easily from the aqueous catalytic media.This study supplies a general method for immobilizing ultrafine Pd nanoparticles into crystalline MOFs and a"green"path for hydrogenation of unsaturated alkene compounds.
查看更多>>摘要：Iron-based catalysts have recognized as the promising candidates for syngas conversion to value-added products.Sodium and sulfur are widely used to refrain the product distribution towards lower olefins.Herein,the synergetic effect between Na and S were investigated by modulating χ-Fe5C2 with Na and/or S.With the characterization of XRD,Raman spectra,FESEM,TEM,TPD,XPS and semi-quantification calculations,we have revealed that when Na and S are added simultaneously,Na tends to activate the deactivated iron sites by S through electron transfer while the formation of long-chain products were weakened.We also demonstrated that sequential loading Na and S would not result in such synergetic effect because of the overlarge intimacy between both elements.This work emphasizes the significance of the synergetic effect of muti-promotors in such a kind of heterogenous catalysis.
查看更多>>摘要：A series of hybrid catalysts with different catalytic bed dispositions(layer bed and simple random mixture)of Cu-ZnO-Al2O3 and SAPO-34 have been adopted and evaluated in syngas conversion into light C2-C4 hydrocarbons.An effect of the proximity between the two solids on the CO hydrogenation activity was demonstrated.A sphere contact quantification model was developed to estimate the concentration of contact between them for any simple random mixture.Comparing the evolution of gain of CO conversion(or hydrocarbon yield)with the theoretical results,it was shown that the density of contact was identified as the key factor for the catalytic performances(contact-activity relationship).Finally,the knowledge of the contact morphology,determined by FEG-SEM,allowed proposing the NH3-TPD as method characterizing the concentration of contact.
查看更多>>摘要：A coated Z-scheme NaGdF4:Nd~(3),Yb~(3),Tm~(3)@CdS-Pd@NiO photocatalyst with core-shell structure is prepared by hydrothermal and coprecipitation methods.NaGdF4:Nd~(3),Yb~(3),Tm~(3)as excellent up-conversion luminescent material can convert infrared light into visible light,broadening the light response range of CdS.Pd nanorods act as conductive channels and co-catalysts,leading to successful construction of tided photocatalyst,increasing contact area between two monomer photocatalysts,promoting transfer of photo-generated electrons.It also provides a large oxidation surface for organic pollutant degradation.The performance of prepared photocatalyst is assessed by Congo red degradation and hydrogen production.The emission spectrum and energy conversion mechanism of NaGdF4:Nd~(3),Yb~(3),Tm~(3)are investigated.The photocatalyst with 3:1 NaGdF4:Nd~(3),Yb~(3),Tm~(3)@CdS-Pd and NiO mass ratio has a preeminent activity.Congo red degradation ratio and hydrogen pro-duction amount reach 92.48% and 653.06 μmol/g,respectively,under simulated sunlight irradiation for 180 min.The possible mechanism of organic pollutant degradation with synchronous hydrogen production caused by titled photocatalyst is proposed.
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