CO氧化不仅具有重要的实用价值,而且在基础研究中被用于考察反应机理及催化剂结构敏感性等一些重要问题,因此,该反应在催化领域中具有重要意义. Pt基催化剂被广泛应用于CO氧化反应.其催化活性取决于催化剂的制备方法.其中,碱金属如Na、K等助剂的添加可有效促进催化活性,红外光谱证据表明,其促进作用在于碱金属的添加可降低CO与表面Pt原子的相互作用.尽管如此,催化剂上反应动力学证据却十分缺乏.反应动力学的研究可以提供一些本证反应信息如反应基元步骤、反应速率表达式以及反应机理等.通过对比不同催化剂之间的反应动力学行为,可以进一步解释碱金属对催化剂结构以及反应行为的影响.因此在本工作中,我们制备了一系列以K为助剂的Pt/Al2O3催化剂,并进行了CO氧化的反应动力学研究,考察了助剂对CO反应级数和反应活化能的影响.结合原位红外光谱表征,进一步揭示了助剂在反应中的作用.通过对比不同Pt和K含量的催化剂上CO氧化反应活性,我们发现, K的添加能促进反应活性,且随着催化剂中K含量的增加,促进程度越明显.例如,0.42K-2Pt/Al2O3上T50温度比对应的2Pt/Al2O3降低了30oC.不同催化剂上CO氧化的反应动力学实验表明,反应速率随着CO的分压的增加而降低；但随着O2分压的增加而增大.幂函数反应速率表达式推导得到的反应级数发现,对于含K的催化剂其CO的反应级数(约为–0.2)明显比不含K的催化剂(约为–0.5)中高,说明K的添加减弱了CO与表面Pt原子之间的吸附能力.但对O2的反应级数影响较小.例如：在0.42K-2.0Pt/Al2O3上反应速率表达式为r =6.55′10–7pco–0.22po20.63；而在2.0Pt/Al2O3上为r =2.56′10–7pco–0.53po20.70.表观反应活化能的计算表明,含K的催化剂上表观反应活化能较低,进一步说明K的添加有利于反应进行.根据反应速率表达式,我们进行了基元步骤的推导,并计算了反应动力学参数.结果发现,与不含K的催化剂相比,含K的催化剂中本征反应速率常数明显增加,而CO吸附平衡常数降低了一半,表明K的存在使CO在Pt表面上的覆盖度降低.我们还通过原位红外光谱对比了催化剂上CO吸附行为的差异.数据表明,与不含K的催化剂相比, K的添加一方面降低了CO在催化剂表面的吸附量(峰面积变小)；另一方面显著降低了CO在Pt表面上的脱附温度,说明两者之间的相互作用力减弱.综上所述,通过反应动力学和红外光谱实验,我们认为K助剂与表面Pt原子相互作用后生成了较为稳定的Pt–O–K物种.尽管该物种的具体结构目前还不明确,但我们的实验证据表明,该物种的存在可以有效减弱CO与表面Pt原子之间的相互作用,降低CO的表面覆盖度并有利于O2在Pt表面的竞争吸附,从而降低了表面吸附的CO与O2之间反应的能垒,促进了反应性能.
A series of K‐promoted Pt/Al2O3 catalysts were tested for CO oxidation. It was found that the addi‐tion of K significantly enhanced the activity. A detailed kinetic study showed that the activation energies of the K‐containing catalysts were lower than those of the K‐free ones, particularly for catalysts with high Pt contents (51.6 kJ/mol for 0.42K‐2.0Pt/Al2O3 and 63.6 kJ/mol for 2.0Pt/Al2O3). The CO reaction orders were higher for the K‐containing catalysts (about?0.2) than for the K‐free ones (about?0.5), with the former having much lower equilibrium constants for CO adsorption than the latter. In situ Fourier‐transform infrared spectroscopy showed that surface CO desorption from the 0.42K‐2.0Pt/Al2O3 catalyst was easier than from 2.0Pt/Al2O3. The promoting effect of K was therefore caused by weakening of the interactions between CO and surface Pt atoms. This decreased coverage of the catalyst with CO and facilitated competitive O2 chemisorption on the Pt surface, and significantly lowered the reaction barrier between chemisorbed CO and O2 species.
参考文献
| [1] | Schryer D R;Upchurch B T;Sidney B D;Brown K G Hoflund G B Herz R K .[J].Journal of Catalysis,1991,130:314. |
| [2] | Yuan Y Z;Kozlova A P;Asakura K;Wan H L Tsai K Iwasawa Y .[J].Journal of Catalysis,1997,170:191. |
| [3] | Haruta M;Kobayashi T;Sano H;Yamada N .[J].CHEMISTRY LETTERS,1987,16:405. |
| [4] | Haruta M;Tsubota S;Kobayashi T;Kageyama H Genet M J Delmon B .[J].Journal of Catalysis,1993,144:175. |
| [5] | Santos V P;Carabineiro S A C;Bakker J J W;Soares O S G P Chen X Pereira M F R Orfao J J M Figueiredo J L Gascon J Kapteijn F .[J].Journal of Catalysis,2014,309:58. |
| [6] | Tost A;Widmann D;Behm R J .[J].Journal of Catalysis,2009,266:299. |
| [7] | Maeda Y;Iizuka Y;Kohyama M .[J].Journal of the American Chemical Society,2013,135:906. |
| [8] | Fujitani T;Nakamura I .[J].ANGEWANDTE CHEMIE-INTERNATIONAL EDITION,2011,50:10144. |
| [9] | Wu Z L;Jiang D E;Mann A K P;Mullins D R Qiao Z A Allard L F Zeng C J Jin R C Overbury S H .[J].Journal of the American Chemical Society,2014,136:6111. |
| [10] | Schryer D R;Upchurch B T;Van Norman J D;Brown K G Schryer J .[J].Journal of Catalysis,1990,122:193. |
| [11] | McClure S M;Goodman D W .[J].CHEMICAL PHYSICS LETTERS,2009,469:1. |
| [12] | Liu H H;Wang Y;Jia A P;Wang S Y Luo M F Lu J Q .[J].Applied Surface Sinence,2014,314:725. |
| [13] | 徐红,傅强,包信和.Pt-表层限域的表面FeOx结构用于低温CO氧化反应[J].催化学报,2013(11):2029-2035. |
| [14] | Fernandez-Garcia M;Martinez-Arias A;Salamanca L N;Coronado J M Anderson J A Conesa J C Soria J .[J].Journal of Catalysis,1999,187:474. |
| [15] | Faticanti M;Cioffi N;De Rossi S;Ditaranto N Porta P Sabbatini L Bleve-Zacheo T .[J].Applied Catalysis B:Environmental,2005,60:73. |
| [16] | Meng L;Jia A P;Lu J Q;Luo L F Huang W X Luo M F .[J].J Phys Chem C,2011,115:19789. |
| [17] | Liu W;Flytzani-Stephanopoulos M .[J].Journal of Catalysis,1995,153:317. |
| [18] | Martinez-Arias A;Fernandez-Garcia M;Galvez O;Coronado J M Anderson J A Conesa J C Soria J Munuera G .[J].Journal of Catalysis,2000,195:207. |
| [19] | Luo M F;Ma J M;Lu J Q;Song Y P, Wang Y.J .[J].Journal of Catalysis,2014,207:246:52. |
| [20] | Jia A P;Hu G S;Meng L;Xie Y L Lu J Q Luo M F .[J].Journal of Catalysis,2012,289:199. |
| [21] | 孙敬方,张雷,葛成艳,汤常金,董林.固相浸渍法和湿浸渍法制备CuO/CeO2催化剂及其CO氧化性能的对比研究[J].催化学报,2014(08):1347-1358. |
| [22] | 陈国星,李巧灵,魏育才,方维平,杨意泉.镍促进CuO-CeO2催化剂的结构表征及低温CO氧化活性[J].催化学报,2013(02):322-329. |
| [23] | Xie X W;Li Y;Liu Z Q;Haruta M Shen W J .[J].NATURE,2009,458:746. |
| [24] | 余立波;赵娇娇;韩雪;张燕 秦秀波 王宝义 .[J].催化学报,2013,34:283. |
| [25] | Qadir K;Kim S H;Kim S M;Ha H Park J Y .[J].J Phys Chem C,2012,116:24054. |
| [26] | Liu L Q;Zhou F;Wang L G;Qi X J Shi F Deng Y Q .[J].Journal of Catalysis,2010,274:1. |
| [27] | Qiao B T;Wang A Q;Yang X F;Allard L F Jiang Z Cui Y T Liu J Y Li J Zhang T .[J].Nature Chem,2011,3:634. |
| [28] | Kuriyama M;Tanaka H;Ito S;Kubota T Miyao T Naito S Tomishi-ge K Kunimori K .[J].Journal of Catalysis,2007,252:39. |
| [29] | Minemura Y;Kuriyama M;Ito S;Tomishige K Kunimori K .[J].CatalCommun,2006,7:623. |
| [30] | Yu X J;Yu W;Li H L;Tu S T Han Y F .[J].Applied Catalysis B:Environmental,2013,140-141:588. |
| [31] | Zhu X L;Hoang T;Lobban L L;Mallinson R G .[J].Catalysis Letters,2009,129:135. |
| [32] | Zhai Y P;Pierre D;Si R;Deng W L Ferrin P Nilekar A U Peng G W Herron J A Bell D C Saltsburg H Mavrikakis M Flytza-ni-Stephanopoulos M .[J].SCIENCE,2010,329:1633. |
| [33] | Pigos J M;Brooks C J;Jacobs G;Davis B H .[J].Applied Catalysis A:General,2007,319:47. |
| [34] | Zhang C B;Liu F D;Zhai Y P;Ariga H Yi N Liu Y Q Asakura K Flytzani-Stephanopoulos M He H .[J].ANGEWANDTE CHEMIE-INTERNATIONAL EDITION,2012,51:9628. |
| [35] | Wang Y;Liu H H;Wang S Y;Luo M F Lu J Q .[J].Journal of Catalysis,2014,311:314. |
| [36] | Fogler H S.Elements of Chemical Reaction Engineering[M].Pearson Education Inc,2006:839. |
| [37] | Shacham M;Cutlip M B;Elly M.[J].Polymath Copyright,2006 |
| [38] | [OL].http://www.polymath-software.com |
| [39] | García-Dieguez M;Pieta I S;Herrera M C;Larrubia M A Malpartida I Alemany L J .[J].Catalysis Today,2010,149:380. |
| [40] | Corro G;Cano C;Fierro J L G .[J].Journal of Molecular Catalysis A:Chemical,2010,315:35. |
| [41] | Machocki A;Ioannides T;Stasinska B;Gac W Avgouropoulos G Delimaris D Grzegorczyk W Pasieczna S .[J].Journal of Catalysis,2004,227:282. |
| [42] | Allian A D;Takanabe K;Fujdala K L;Hao X H Truex T J Cai J Buda C Neurock M Iglesia E .[J].Journal of the American Chemical Society,2011,133:4498. |
| [43] | Gracia F J;Bollmann L;Wolf E E;Miller J T,Kropf A.J .[J].Journal of Catalysis,2003,220:382. |
| [44] | Li N;Chen Q Y;Luo L F;Huang W X,Luo M F,Hu G S,Lu J.Q .[J].Applied Catalysis B:Environmental,2013,142-143:523. |
| [45] | Bourane A;Bianchi D .[J].Journal of Catalysis,2001,202:34. |
| [46] | Djéga-Mariadassou G;Boudart M .[J].Journal of Catalysis,2003,216:89. |
| [47] | Derrouiche S;Gravejat P;Bassou B;Bianchi D .[J].Applied Surface Sinence,2007,253:5894. |
| [48] | Chafik T;Dulaurent O;Gass J L;Bianchi D .[J].Journal of Catalysis,1998,179:503. |
| [49] | Alexeev O S;Chin S Y;Engelhard M H;Ortiz-Soto L Amiridis M D .[J].Journal of Physical Chemistry B,2005,109:23430. |
| [50] | Xu L S;Ma Y S;Zhang Y L;Jiang Z Q Huang W X .[J].Journal of the American Chemical Society,2009,131:16366. |
- 下载量()
- 访问量()
- 您的评分：
-
10%
-
20%
-
30%
-
40%
-
50%