负载液pH对Co-Mo/MgO-Al_2O_3催化剂水煤气变换性能的影响
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摘要
以MgO-Al_2O_3复合氧化物为载体,调节负载液的pH=3,7,10,负载Co-Mo活性组分制备了耐硫水煤气变换Co-Mo/MgO-Al_2O _3系列催化剂,并进行了催化性能评价实验。采用H_2-TPR和激光拉曼光谱(LRS)方法对系列催化剂进行了表征,考察了负载液的酸碱性对Co-Mo活性组分在MgO-Al_2O_3复合氧化物载体分散和表面物种形成的影响。实验结果表明,随着不同pH负载液的加入,载体表面的电化性质发生变化,从而影响载体与Co-Mo活性组分、Co和Mo组分之间的相互作用,改变了活性组分Co和Mo在载体表面的分散度和表面物种的形态;当负载液pH=3,7时,Mo与载体的相互作用较强,而当负载液pH=10时,在氧化态催化剂中有利于形成八面体结构Mo物种,经过升温硫化后,催化剂表面形成更多O_xMo S~(2-)_(4-x)和Mo S_2物种。
The effect of the acid and base properties of impregnant on the performance of Co-Mo/MgO-Al_2O_3 catalyst for water-gas shift reaction was studied by means of H_2-TPR and laser Raman spectroscopy(LRS)techniques.The results showed that molybdete anions were adsorbed preferentially on the surface of the support with positive charge when the pH of the impregnant was controlled at 3or 7(this condition favors the interaction between support and molybdenum species),while cobalt cations were adsorbed preferentially on the surface of the support with negative charge when the pH of the impregnant was adjusted to 10(this condition benefits weakening the interaction between support and molybdenum species,which is propitious to form octahedron molybdenum species easy to be reduced).The formation of more O_xMoS~(2-)_(4-x) and MoS_2 species was found to be responsible for high catalytic activity of the catalyst thus prepared.
The effect of the acid and base properties of impregnant on the performance of Co-Mo/MgO-Al_2O_3 catalyst for water-gas shift reaction was studied by means of H_2-TPR and laser Raman spectroscopy(LRS)techniques.The results showed that molybdete anions were adsorbed preferentially on the surface of the support with positive charge when the pH of the impregnant was controlled at 3or 7(this condition favors the interaction between support and molybdenum species),while cobalt cations were adsorbed preferentially on the surface of the support with negative charge when the pH of the impregnant was adjusted to 10(this condition benefits weakening the interaction between support and molybdenum species,which is propitious to form octahedron molybdenum species easy to be reduced).The formation of more O_xMoS~(2-)_(4-x) and MoS_2 species was found to be responsible for high catalytic activity of the catalyst thus prepared.
引文
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[2]Pawelec B,Halachev T,Olivas A,et al.Impact of preparation method and support modification on the activity of mesoporous hydrotreating CoMo catalysts[J].Appl Catal,A,2008,348(1):30-41.
[3]甄开吉,王国甲,毕颖丽,等.催化作用基础[M].3版.北京:北京科学出版社,2005:47-50.
[4]罗锡辉,何金海.载体、金属-载体相互作用与多相催化剂的制备[J].石油学报:石油加工,2003,16(3):1-13.
[5]赵永祥,安立敦.负载型贵金属催化剂的制备化学--载体等电点对Pd/Al2O3催化剂结构与催化性能的影响[J].分子催化,1994,8(1):29-35.
[6]孟明,林培琰,伏义路,等.氧化态Co/γ-Al2O3催化剂的结构与反应性能研究:钴物种微观结构的XAFS表征[J].分子催化,2000,14(3):161-165.
[7]邱滔,李桂勇,吕新宇.类水滑石催化氰乙酸甲酯与乙醇的酯交换反应[J].石油化工,2008,37(3):272-276.
[8]Reymond J P,Kolenda F.Estimation of the point of zero charge of simple and mixed oxides by mass titration[J].Powder Technol,1999,103(1):30-36.
[9]Hui Ming,Baker B G.Characterization of cobalt Fischer-Tropsch catalystsⅠ.Unpromoted cobalt-silica gel catalysts[J].Appl Catal,A,1995,123(1):23-36.
[10]Lian Yixin,Wang Huifang,Zheng Quanxing,et al.The effect of Mg/Al atom ratio of the compound oxide support on catalytic performance of Co-Mo based catalyst for water-gas shift reaction[J].J Nat Gas Chem,2009,18(2):161-166.
[11]赵红霞,朱柘权,陈建刚,等.浸渍溶液pH值对Co/SiO2催化剂催化F-T合成反应的影响[J].催化学报,2004,25(4):289-292.
[12]耿云峰,王希涛,钟顺和.MoO3/SiO2催化剂的异丁烷选择氧化反应性能[J].分子催化,2002,16(4):273-278.
[13]Kalu?a L,GulkováD,Vít Z,et al.Effect of support type on the magnitude of synergism and promotion in Co Mo sulphide hydrodesulphurisation catalyst[J].Appl Catal,A,2007,324(1):30-35.
[14]万江,刘够生,宋兴福,等.Co-Mo/γ-Al2O3耐硫脱氧催化剂的TPD-TPR研究[J].高校化学工程学报,2005,19(5):703-707.
[15]魏昭彬,魏成栋,辛勤.MoO3/TiO2-Al2O3催化剂表面结构的LRS研究[J].物理化学学报,1992,82(2):261-268.
[16]Li Zhengping,Gao Lian,Zheng Shan.Investigation of the dispersion of MoO3 onto the support of mesoporous silica MCM-41[J].Appl Catal,A,2002,236(1/2):163-171.
[17]Li Zhongrui,Fu Yilu,Bao Jun,et al.Effect of cobalt promoter on Co-Mo-K/C catalysts used for mixed alcohol synthesis[J].Appl Catal,A,2001,220(1):21-30.
[18]González-Cortés S L,Xiao Tiancun,Costa R M F J,et al.Urea-organic matrix method:An alternative approach to prepare Co-MoS2/γ-Al2O3 HDS catalyst[J].Appl Catal,A,2004,270(1/2):209-222.