不同Pd/Ag配比Pd-Ag/Al_2O_3催化乙炔加氢微观反应动力学分析
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摘要
乙炔加氢是乙烯工业中的重要精制反应。以α-Al_2O_3作为载体,采用分步等量浸渍法制备了不同Pd/Ag配比的加氢催化剂,使用N2物理吸附、XRD、ICP、XPS、TEM和CO化学吸附等手段表征催化剂的结构和组成,根据正交实验设计方案进行动力学实验,建立了微观反应动力学模型,并根据动力学模拟结果和动力学参数值的变化分析了Ag助剂含量对乙炔加氢反应动力学的影响。研究结果表明,以Pd-Ag催化剂上碳二加氢的DFT计算结果为基础参数来源,经过吸脱附步骤活化能的优化,微观反应动力学模型可以很好地模拟不同Pd/Ag配比催化剂上的乙炔加氢反应动力学结果;在所研究范围内,各催化剂上加氢反应的表面最丰物种皆为C2H4*,速率控制步骤为乙烯基加氢,不会随着Ag含量的不同发生变化;但是Ag含量的增加显著降低了氢气脱附活化能,提高了乙烯的选择性,这可能与Ag含量的提高增加了催化剂表面Ag和Pd之间的电子转移现象有关。
Selective acetylene hydrogenation is an important purifying reaction in ethylene industry. Pd-Ag/α-Al_2O_3 catalysts with different Pd/Ag ratios were prepared by stepwise incipient wetness impregnation method and characterized for structure and composition by N2-physisorption,XRD,ICP,XPS,TEM and CO chemisorption. A microkinetic model of acetylene hydrogenation over these catalysts was established from a fractional factorial design of experiment and effects of Ag amount on the hydrogenation kinetics were analyzed through microkinetic simulation and parameter value change. After values for basic parameters used DFT calculation results of C2 hydrogenation over Pt-Ag catalysts and activation energies optimized by adsorption-desorption steps, the microkinetic model could fit kinetic experiment results quite well on acetylene hydrogenation over all catalysts of various Pt-Ag ratios. The study showed that C2 H4* was the most abundant surface species and vinyl hydrogenation was rate control step, which did not change with increase of Ag content. However, the increase of Ag greatly reduced activation energy of hydrogen desorption and improved ethylene selectivity. This phenomenon might be correlated to enhancement of electron transfer from Ag to Pd on the catalyst surface upon increase of Ag content.
Selective acetylene hydrogenation is an important purifying reaction in ethylene industry. Pd-Ag/α-Al_2O_3 catalysts with different Pd/Ag ratios were prepared by stepwise incipient wetness impregnation method and characterized for structure and composition by N2-physisorption,XRD,ICP,XPS,TEM and CO chemisorption. A microkinetic model of acetylene hydrogenation over these catalysts was established from a fractional factorial design of experiment and effects of Ag amount on the hydrogenation kinetics were analyzed through microkinetic simulation and parameter value change. After values for basic parameters used DFT calculation results of C2 hydrogenation over Pt-Ag catalysts and activation energies optimized by adsorption-desorption steps, the microkinetic model could fit kinetic experiment results quite well on acetylene hydrogenation over all catalysts of various Pt-Ag ratios. The study showed that C2 H4* was the most abundant surface species and vinyl hydrogenation was rate control step, which did not change with increase of Ag content. However, the increase of Ag greatly reduced activation energy of hydrogen desorption and improved ethylene selectivity. This phenomenon might be correlated to enhancement of electron transfer from Ag to Pd on the catalyst surface upon increase of Ag content.
引文
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[21]BOND G C,WELLS P B.The hydrogenation of acetylene(Ⅱ):The reaction of acetylene with hydrogen catalyzed by alumina-supported palladium[J].Journal of Catalysis,1966,5(1):65-73.
[22]PEI G X,LIU X Y,WANG A,et al.Ag alloyed Pd single-atom catalysts for efficient selective hydrogenation of acetylene to ethylene in excess ethylene[J].ACS Catalysis,2015,5(6):3717-3725.
[23]BORODZINSKI A,CYBULSKI A.The kinetic model of hydrogenation of acetylene-ethylene mixtures over palladium surface covered by carbonaceous deposits[J].Applied Catalysis A:General,2000,198(1/2):51-56.
[24]LYNGGAARD H,ANDREASEN A,STEGELMANN C,et al.Analysis of simple kinetic models in heterogeneous catalysis[J].Progress in Surface Science,2004,77(3/4):71-137.
[25]KHAN N A,SHAIKHUTDINOV S,FREUND H J.Acetylene and ethylene hydrogenation on alumina supported Pd-Ag model catalysts[J].Catalysis Letters,2006,108(3/4):159-164.
[26]SHETH P A,NEUROCK M,SMITH C M.First-principles analysis of the effects of alloying Pd with Ag for the catalytic hydrogenation of acetylene-ethylene mixtures[J].Journal of Physical Chemistry B,2005,109(25):12449-12466.
[27]MEI D H,NEUROCK M,SMITH C M.Hydrogenation of acetylene-ethylene mixtures over Pd and Pd-Ag alloys:first-principles-based kinetic Monte Carlo simulations[J].Journal of Catalysis,2009,268(2):181-195.
[2]BOS A N R,WESTERTERP K R.Mechanism and kinetics of selective hydrogenation of ethyne and ethene[J].Chemical Engineering and Processing,1993,32(1):1-7.
[3]李立新.乙炔前加氢反应器运行稳定性的研究[J].化学反应工程与工艺,2004,20(1):47-52.LI L X.Analysis on the stability of the front-end acetylene hydrogenation reactor[J].Chemical Reaction Engineering and Technology,2004,20(1):47-52.
[4]PACHULSKI A,SCH?DEL R,CLAUS P.Performance and regeneration studies of Pd-Ag/Al2O3 catalysts for the selective hydrogenation of acetylene[J].Applied Catalysis A:General,2011,400(1/2):14-24.
[5]KONHOM S,MEKASUWANDUMRONG O,PRASERTHDAM P,et al.Improvement of Pd/Al2O3 catalyst performance in selective acetylene hydrogenation using mixed phases Al2O3 support[J].Catalysis Communications,2008,10(1):86-91.
[6]KIM S K,LEE J H,AHN I Y,et al.Performance of Cu-promoted Pd catalysts prepared by adding Cu using a surface redox method in acetylene hydrogenation[J].Applied Catalysis A:General,2011,401(1/2):12-19.
[7]FENG J,LIU Y,YIN M,et al.Preparation and structure-property relationships of supported trimetallic Pd Au Ag catalysts for the selective hydrogenation of acetylene[J].Journal of Catalysis,2016,344:854-864.
[8]SMIRNOVA N S,SHLYAPIN D A,SHITOVA N B,et al.EXAFS study of Pd/Sibunit and Pd-Ga/Sibunit catalysts for liquid-phase hydrogenation of acetylene to ethylene[J].Journal of Molecular Catalysis A:Chemical,2015,403:10-14.
[9]戴伟.新型碳二馏分选择加氢BC-H-20催化剂的设计与开发[J].石油化工,2004,33:147-148.DAI W.Design and development of novel C2 fraction selective hydrogenation BC-H-20 catalyst[J].Petrochemical Technology,2004,33:147-148.
[10]ZHU S Y,HOU R J,WANG T F.Effects of supports and promoter Ag on Pd catalysts for selective hydrogenation of acetylene[J].The Chinese Journal of Process Engineering,2012,12(3):489-496.
[11]KUHN M,LUCAS M,CLAUS P.Long-time stability vs deactivation of Pd-Ag/Al2O3 egg-shell catalysts in selective hydrogenation of acetylene[J].Industrial&Engineering Chemistry Research,2015,54(26):6683-6691.
[12]董文寰,李斯琴.新型C2馏分加氢除炔催化剂的制备和应用[J].石油化工,2005,34(12):1186-1189.DONG W H,LI S Q.Preparation and application of novel C2 fraction selective hydrogenation catalyst[J].Petrochemical Technology,2005,34(12):1186-1189.
[13]DUMESIC J A,TREVINO A A,MILLIGAN B A,et al.A kinetic modeling approach to the design of catalysts:formulation of a catalyst design advisory program[J].Industrial&Engineering Chemistry Research,1987,26(7):1399-1407.
[14]STUDT F,ABILD-PEDERSEN F,BLIGAARD T,et al.Identification of non-precious metal alloy catalysts for selective hydrogenation of acetylene[J].Science,2008,320(5881):1320-1322.
[15]SELLERS H,GISLASON J.Adsorption and desorption rate constants for small molecules on metal surfaces:an example of Trouton’s rule[J].Surface Science,1999,426(2):147-53.
[16]SELLERS H.Entropies of desorption from temperature programmed desorption data:?trends and applications to rate constant determinations[J].Journal of Physical Chemistry B,2003,107(37):10206-10208.
[17]MITSUI T,ROSE M K,FOMIN E,et al.Hydrogen adsorption and diffusion on Pd(111)[J].Surface Science,2003,540(1):5-11.
[18]杜梅西克J A.多相催化微观动力学[M].沈俭一,译.北京:国防工业出版社,1998.DUMESIC J A.The Microkinetics of Heterogeneous Catalysis[M].SHEN J Y,trans.Beijing:National Defense Industry Press,1998.
[19]王新宇,隋志军,朱贻安,等.Pd/α-Al2O3催化乙炔选择性加氢微观反应动力学[J].化学反应工程与工艺,2015,31(4):322-329.WANG X Y,SUI Z J,ZHU Y A,et al.Microkinetics of acetylene selective hydrogenation over Pd/Al2O3 catalyst[J].Chemical Reaction Engineering and Technology,2015,31(4):322-329.
[20]庞洪强,隋志军,朱贻安,等.不同粒径Pd/Al2O3催化乙炔加氢反应微观动力学分析[J].化工学报,2016,67(9):3692-3698.PANG H Q,SUI Z J,ZHU Y A,et al.The microkinetics analysis of acetylene hydrogenation over Pd/Al2O3 catalyst with different particle sizes[J].CIESC Journal,2016,67(9):3692-3698.
[21]BOND G C,WELLS P B.The hydrogenation of acetylene(Ⅱ):The reaction of acetylene with hydrogen catalyzed by alumina-supported palladium[J].Journal of Catalysis,1966,5(1):65-73.
[22]PEI G X,LIU X Y,WANG A,et al.Ag alloyed Pd single-atom catalysts for efficient selective hydrogenation of acetylene to ethylene in excess ethylene[J].ACS Catalysis,2015,5(6):3717-3725.
[23]BORODZINSKI A,CYBULSKI A.The kinetic model of hydrogenation of acetylene-ethylene mixtures over palladium surface covered by carbonaceous deposits[J].Applied Catalysis A:General,2000,198(1/2):51-56.
[24]LYNGGAARD H,ANDREASEN A,STEGELMANN C,et al.Analysis of simple kinetic models in heterogeneous catalysis[J].Progress in Surface Science,2004,77(3/4):71-137.
[25]KHAN N A,SHAIKHUTDINOV S,FREUND H J.Acetylene and ethylene hydrogenation on alumina supported Pd-Ag model catalysts[J].Catalysis Letters,2006,108(3/4):159-164.
[26]SHETH P A,NEUROCK M,SMITH C M.First-principles analysis of the effects of alloying Pd with Ag for the catalytic hydrogenation of acetylene-ethylene mixtures[J].Journal of Physical Chemistry B,2005,109(25):12449-12466.
[27]MEI D H,NEUROCK M,SMITH C M.Hydrogenation of acetylene-ethylene mixtures over Pd and Pd-Ag alloys:first-principles-based kinetic Monte Carlo simulations[J].Journal of Catalysis,2009,268(2):181-195.