磷化钨催化转化纤维素制乙二醇

催化挲报2010Chinese Journal of CatalysisVol 31 No 8文章编号:0253-9837(2010)08-0928-国际版DOI:10.1016/S1872-2067(10)60104-0研究快讯:928-932磷化钨催化转化纤维素制乙二醇赵冠鸿2,郑明远!,王爱琴!,张涛中国科学院大连化学物理研究所催化基础国家重点实验室,辽宁大连1160232中国科学院研究生院,北京100049摘要:首次将磷化钨(WP)催化剂应用于纤维素的催化转化反应.结果表明,与碳化钨催化剂类似,WP催化剂也可高效地实现纤维素转化.在H2初始压力为6MPa,反应温度为245℃C时,20%wPAC(活性炭)催化纤维素高选择性地生成乙二醇,其收率为254mol%.2%镍的加入使得该催化剂上乙二醇收率增至46.0mol1%,表明Ni与WP之间存在着明显的协同作用关键词:生物质;纤维素;磷化钨;乙二醇中图分类号:O643文献标识码:ACatalytic Conversion of Cellulose to Ethylene Glycol overTungsten Phosphide catalystsZHAo Guanhong, ZHENG Mingyuan, WANG Aiqin, ZHANG TaoState Key laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, ChinaGraduate University of Chinese Academy of Sciences, Beijing 100049, ChinaAbstract: Tungsten phosphide(wP) showed good activity in the selective conversion of cellulose to ethy lene glycol (EG). At a H2 initialpressure of 6 MPa and temperature of 245 C, EG yield reached 25. 4 mol% over 20%WP/AC (activated carbon)and 46.0 mol%over2%Ni-20%WP/AC, which demonstrated a remarkable synergy between Ni and WPKey words: biomass; cellulose; tungsten phosphide; ethylene glycol随着化石能源的日渐枯竭和气候环境的不断恶于贵金属的催化性质,将纤维素高选择性地转化为化,寻找清洁的替代能源成为人类的重要课题.由多元醇812.特别是在活性炭(AC)以及介孔炭负于生物质具有碳平衡和可再生的优点,在新能源开载的镍-碳化钨(W2C)催化剂上,纤维素高选择性地发诸多途径中,由生物质转化为能源化学品和大宗转化为乙二醇(EG,其收率最高可达75wt%0.为平台化合物备受人们关注.木质纤维素是地球上最了进一步阐明W2C在该反应中独特的催化作用,我丰富的生物质资源,广泛存在于各种农业废弃物中,们使用金属Ni-W的组合代替Ni-W2C催化剂,发现但它的结构致密复杂,因此,实现其高效、特别是高其仍可高选择性地催化纤维素转化为EG.而以选择性转化是一项极具挑战性的课题.在各种可能磷化镍为催化剂时,纤维素主要转化为山梨醇,而非的转化途径中”,利用固体催化剂催化转化木质纤乙二醇12.由此可见,W物种在纤维素的CC键选维素具有反应条件较温和、选择性高、催化剂易于择性断裂过程中起着非常关键的作用,而另一活性回收、环境友好等优点,因而成为近年来的研究热点组分Ni则主要起加氢作用.为进一步验证上述推之-【57断,本文分别制备了AC和SiO2负载的磷化钨本课题组曾利用过渡金属碳化物和磷化物类似(WP)催化剂中国煤化工催化行为收稿日期:2010-06-24CNMHG联系人:张涛.Tel:(0411)84379015;Fax:(0411)84685940;E-mai: taizhang @dicp.ac.cr基金来源:国家重点基础研究发展计划(973计划,2009CB26102);国家自然科学基金(20903089,20773124)本文的英文电子版由 Elsevier出版社在 Science Direct上出版htp:ww. sciencedirect. com/science/journal18722067)www.chxb.cr赵冠鸿等:磷化钨催化转化纤维素制乙二醇929采用还原磷酸盐法制备WP催化剂13.14.配制定浓度的偏钨酸铵(AMT)和(NH4)2HPO4溶液,7 w,C等体积浸渍于AC( Norit,20-40目,比表面积709Ni?P20%WP/ACm2/g)或SO2(青岛海洋化工厂,20-40目,比表面积L人人人455m2/g)上,于120℃C干燥12h,在H2中首先以会2%Ni-20%WP/A55C/min升至350°C,然后以1C/min升至850°C,并保持1h,H2空速(GHSV)为12000h1.还原20%WP/SIO结束后,待温度降至室温,通入1%02-99%N2混合气钝化4h.采用N(NO3)2,(NH4)2HPO4和AMT共浸60渍的方法制备Nⅰ-WP样品,除了最终还原温度为图1不同磷化钨催化剂的XRD谱650C之外,其他过程同上.制得的催化剂中WFig. 1. XRD patterns of different tungsten phosphide catalystsNi的理论含量分别为20wt%和2wt%使用PW3040/60 X Pert Pro( PANalytical)型见,20%WPAC催化剂上出现典型的WP特征峰以Ⅹ射线衍射仪对催化剂物相进行分析.催化剂的及少量的W2C晶相.这是由于在wP高温还原制CO化学吸附实验在法国 Seteram公司的BT2.15型备过程中,炭载体的碳热还原作用使催化剂中形成微量热量计上进行5.测试前,催化剂在H2中于了W2C物相.而在20%WPSO2催化剂上,只观察650℃C原位还原1h.催化剂的透射电镜(TEM)表到一个很微弱的wP特征峰,这可能是由于WP高征在JEM-2000EX型透射电子显微镜上进行.纤维度分散于SO2载体上.CO化学吸附实验表明,素催化转化反应在100m1不锈钢高压釜(Par仪器20% WP/SiO2上的CO吸附量为18.3μmol/g,而公司)中进行.加入0.5g微晶纤维素、0.15g催化20%WP/AC上仅为83μmol/g这进一步表明前者剂和50ml去离子水,搅拌速率为1000rmin,H2初的活性组分分散度更高.TEM结果(未示出)表明始压力为6MPa(室温下).在245℃C反应30min. WP/SIO2样品的WP粒径明显小于wP/AC反应后液体产物用液相色谱仪分析.有机总碳由2%N20%WPAC催化剂主要晶相仍为WP,同时还Elementar Liqui TOC型总碳测定仪测定.反应前后存在少量的W2C和Ni2P物相催化剂上金属流失量由 IRIS Intrepid Il XSP型电各催化剂纤维素催化转化反应结果见表1.由感耦合等离子体发射光谱仪测得.气相产物由气相表可见,在各WP催化剂上,纤维素反应30min后色谱仪分析.反应转化率由反应前后纤维素质量变均完全转化,其中,20%WPAC催化剂上所得的各化求得5.产物收率以反应产物与投入釜内纤维素种多元醇产物中,EG的收率最高,为254mol%,而的各自C的摩尔比计算12六元醇收率则仅为2.3mol%.这与我们早前报道的图1为不同磷化钨催化剂的XRD谱.由图可纤维素在W2CAC催化剂上反应结果十分类似9表1不同催化剂上纤维素的转化率及多元醇的产率Table 1 Results of cellulose conversion and polyol yields over the catalystsYield (mol/%)CatalyConversion(%) Conversion(%)Glycerol EG 1, 2-PG Sorbitol Mannitol Erythritol COz CO86.525.480.561.70.220%WP/AC2.120%WP/AC2%Ni-20%WP/AC87.2946.0640.80.030%NI/AC+20%WP/AC0.8中国煤化工CNMHG20%WP/AC in the 2nd run. 20%WP/AC in the 3rd run ' Cellulose conversion calculated bycelulose velue and after reactioncEllulose conversion calculated by organic carbon in liquid products divided by total carbon of cellulose put into the reactorG--Ethylene glycol; PG--Propylene glycol930催化学报Chin.J.Cua1,2010,31:928932由于20%WPAC催化剂制备过程中载体AC的碳ICP测定结果显示,反应过程中催化剂中的W流失热还原作用而使催化剂中出现少量W2C,这可能对了52wt%.因而,我们推测,催化剂活性的下降与EG的生成起到重要的催化作用.为排除这种影响,W的流失有很大的关系.另外,催化剂表面的部分本文考察了20% WP/SiO2催化剂的反应性能.结果氧化也可能是失活原因之显示,该催化剂性能与WPAC非常类似,纤维素主在纤维素转化为多元醇的过程中,催化剂的加要转化为EG,收率为250mo%这表明WP确实氢能力至关重要10.因此,本文利用Ni来修饰可直接催化纤维素转化为EG相比于我们最近所WP催化剂,以形成更多的加氢活性中心.CO化学报道的磷化镍催化剂12,两者虽然同样是磷化物,吸附测量结果显示,Ni的添加使得20%WP/AC催但在纤维素转化反应中生成的产物却明显不同.纤化剂上CO吸附量由8.3μmolg增至11.9μmol/g维素在磷化镍催化剂上高选择性地生成山梨醇,收纤维素催化转化反应结果表明,Ni的添加使得催化率达484mol%,而在WP催化剂上得到的主要是剂上EG产率显著增至460mol%.当将10%Ni/AC小分子产物EG.结合我们前期对W2C以及金属W和20%WPAC机械混合后用于反应时,EG产率虽催化剂上纤维素催化转化的研究结果8,我们认然较两种催化剂单独使用时有所提高,但远低于为,WP催化剂不仅在纤维素降解转化过程中具有2%N-20%WPAC催化剂.这表明,Ni和W间存在催化加氢作用,同时催化剂中W物种的存在对反应显著的协同作用.一方面,W物种的存在使纤维素物分子内CC键的断裂具有重要的催化作用发生选择性CC断裂而降解为小分子的C2不饱和气相产物分析结果显示,WP催化剂上纤维素化合物;另一方面,WP自身以及Ni等催化加氢活能够转化生成很少量的CO和CO2,但未检测到烃性中心催化不饱和分子加氢反应生成EG.因此,可类产物.通过液体产物中的有机总碳量计算纤维素以通过适宜的加氢组分修饰或借助新的制备方法,转化率为80%-90%,造成反应后出现10‰-20%碳调变催化剂上两种催化能力的相对强弱,使WP催损失的原因尚不清楚化剂在纤维素催化转化为EG的反应中表现出更好通过循环反应考察了20%WP/AC催化剂的稳的催化性能定性.结果表明,循环使用3次后,乙二醇收率由WP催化剂在催化纤维素转化制EG的反应中254mol%降至174mol%.图2为反应后催化剂的表现出了良好的性能,在Ni的促进下,EG产率可以XRD谱.由图可知,使用3次后,虽然WP衍射峰增至460mol%.与W2C催化剂相类似,WP催化剂强度略有下降,但其晶相仍保持良好,没有检测到氧中同样存在两种催化中心的协同作用.Ni作为催化化钨.另一方面,反应后催化剂的CO吸附量由8.3加氢助剂可显著提高EG产率.该结果有助于加深umol/g降为6.4μmolg.液体反应产物中W元素的理解含W催化剂中W在纤维素转化成乙二醇反应中的作用,同时为发展新型廉价的生物质转化催化剂提供有益的参考.After 3rd run参考文献After 2nd runI Lynd L R, Cushman J H, Nichols R J, Wyman C E. Science,1991,251:13After l st run2 Philippidis g P, Smith T K, Wyman C E. Biotechnol Biogs1993.41:8463 Asadullah M, Kaoru F, Keiichi T. Ind Eng Chem, ResFresh 20%WP/AC2001,40:58944 Mohan D, Pittman C U, Steele P H. Energy Fuels, 200620:848中国煤化工Ed,2006,45CNMHG图2新鮮鲜和循环反应后的20%WP/AC催化剂XRD谱6 Yan N, Zhao C, Luo C, Dyson PJ, Liu H C, Kou YJ AmFig 2 XRD patterns of fresh and recycled 20%WP/AC catalystsChem soc,2006,128:8714www.chxb.cr赵冠鸿等:磷化钨催化转化纤维素制乙二醇9317 Luo C, Wang S C, Liu H C Angew Chem, Int Ed, 2007, 46: component mainly promotes catalytic hydrogenation.Tofurther prove this proposition, in this work, we prepared8 JiN Zhang I, Zheng M Y, Wang A Q, Wang H, Wang X D, tungsten phosphide(WP) catalysts supported on AC andChen J G Angew Chem, Int Ed, 2008, 47: 8510silica, and investigated their catalytic behavior in the con9 JiN, Zhang T, Zheng M Y, Wang A Q, Wang H, Wang X Dversion of celluloseShu Y Y, Stottlemyer A L, Chen JG G Catal Today, 2009147:7The preparation of the tungsten phosphide catalysts10 Zhang Y H,Wang A Q, Zhang T. Chem Commun, 2010, 46: comprised three steps [13, 14]: impregnating the support, AC(Norit, 20-40 mesh, ABET 709 m /g) or silica (QingdaoI 1 Zheng MY, Wang A Q, Ji N, Pang J F, Wang X D, ZhangHaiyang Chemical Company, 20-40 mesh, ABET =455 m /g),T. ChemSus chem 2010.3: 63with solutions of ammon2 Ding L N, Wang A Q, Zheng M Y, Zhang T. Chem- (NH4)HPO4, drying the sample at 120"C for 12 h, andSus chem,2010,3:818reduction with a procedure in which the sample was heated3 Shu Y, Oyama S T Carbon, 2005, 43: 1517from room temperature to 350 C at a rate of 5.5 C/min, then14 Clark P, Wang X, Oyama S T J Catal, 2002, 207: 256to 850C at a rate of 1 C/min, and kept at 850C for I h. The5 Li L, Wang X, Shen J, Zhou L, Zhang T. Therm Anal hydrogen gas hourly space velocity(GHSv) was 12 000 hChlorin,2005,82:103After reduction, the phosphide was passivated in 1%O99%N, for 4 h For th英译文tungsten phosphide catalyst, Ni(NO3)2 was co-impregnatedwith AMT and(NH4h2HPO4, which was followed with theEnglish Textprocedure described above, except that thNowadays, fossil energy depletion and climate temperature was 650C. The nominal loadings of tungstenterioration are driving the development of alternative clean and nickel were 20 wt% and 2 wt%, respectivelyenergy sources. Among various potential solutiX-ray diffraction (XRD) patterns were obtained on aconverting of biomass to energy chemicals and building PW3040/60 XPert PRO(PANalytical) diffractometer. COblock materials is regarded as one of the most attractive chemisorption measurement was conducted on a calvet-typeapproaches because of the carbon neutrality and renewablemicrocalorimeter (Seteram BT2 15)described elsewhereproperties of biomass. Lignocellulose, the most abundant [15]. Before the measurement, the catalyst was treated in Hbiomass on earth, is widely available inflow at 650C for I h. Transmission electron microscopywastes. However, the crystalline and compact structure of ( TEM) analysis was performed on a JEM-2000EX (JEOL)cellulose makes it difficult to degrade. It remains a microscope. The catalytic conversion of cellulose(Merck,llenge to efficiently and selectively convert microcrystalline) was performed in a stainless steel autoclavecellulose into valuable chemicals. Among possible routes (Parr Instrument Company, 100 mI)at a H2 pressure of 61-7], the catalytic conversion of lignocellulose with solid MPa(measured at room temperature)and 245 C for 30 mincatalysts has unique advantages such as good selectivity for For each reaction, cellulose(0. 5 g), catalyst(0.15 g),andtarget products, reusability of catalysts, mild reaction deionized water (50 mI)were charged into the reactor andconditions, and environmental friendliness [5-7]stirred at a rate of 1 000 r/min. The liquid products werePreviously, we have reported that cellulose can be coranalyzed by high performance liquid chromatography. Theverted into polyols with high selectivity over transition metal liquid products were also analyzed by the total orcarbide and phosphide catalysts[8-12]. In particular, over carbon (TOC) method on a Elementar Liqui TOCtungsten carbide(W2 C)supported on activated carbon (AC) instrument. The metal loss from the catalyst after reactionand mesoporous carbon and nickel-promoted tungsten car- was determined by inductively coupled plasma(ICP)usingbide catalysts, the highest ethylene glycol (EG) yield ob- an IRIS Intrepid II XSP instrument(Thermo Electrontained was 75 wt%[10]. To unravel the unique role of tung- Corporation). The gas products were analyzed by gassten carbide in the transformation of cellulose to EG. we chromatography. Cellulose conversions were determined byemployed Ni-W bimetallic catalysts instead of Ni-W2C, and the weight change of cellulose before and after the reactionfound that the Ni-w bimetallic catalysts also exhibited high [5, 8]. The yields of polyols were calculated by the carbonactivity and selectivity[11]. In contrast to w-based catalysts, mole ratio of product and cellulose [12]with nickel phosphide catalysts, the main product was sor中国煤化工 alyst20%WPbitol rather than EG [12]. These results suggest that the AC showed typiCNMHGnall amount oftungsten component plays an important role in selectively tungsten carbide was arIeu. wien was ascribed to thecracking the C-c bond of the reactant, while the nickel carbothermal reduction of tungsten by the carbon support to932催化学报Chin.J.Cua1,2010,31:928932form the carbide during the high temperature preparation of The XRD patterns of the spent catalysts( Fig. 2)showed thattungsten phosphide. In contrast, for the silica-supported the WP phase remained well dispersed after three recyclingcatalyst 20%WP/SiO2, only a very weak peak of the WP runs and no tungsten oxide peaks were seen On the otherphase was observed. The absence of most of the diffraction hand, a comparison of the Co uptake amounts before andpeaks of WP from the 20%WP/SiO2 catalyst suggested a after reaction indicated that the co uptake had slightly de-high dispersion of WP on the silica support. The CO ad- creased (6.4 umol/g) after the reaction. The ICP analysis ofsorption measurement showed a CO uptake of 18.3 umol/g the liquid products showed that 5.2 wt% tungsten from theby 20%WP/SiO2, which was more than twice that by catalyst was leached into the solution after reaction. This20%WP/AC (8.3 umol/g), which further demonstrated that may account for the decrease in catalytic activity. In addition,tungsten phosphide had a higher dispersion on the partial oxidization of the active sites on the catalyst may be20%WP/SiO2 catalyst. The TEM images (not shown) another reason for the deactivationshowed that the particle size of tungsten phosphide onActivity for catalytic hydrogenation is necessary for a20%WP/SiO2 was smaller than on 20%WP/AC. On the catalyst for cellulose conversion to polyols [10, 11]. Thus, we2%Ni-20%WP/AC catalyst, the main phase was still WP, attempted to modify the tungsten phosphide catalyst withwith small amounts of w,c and ni,pnickel to provide more hydrogenating sites on the catalystsThe catalytic conversions of cellulose over the various The Co chemisorption measurement showed that the COcatalysts are listed in Table 1. Over all the tungsten uptake amount over 2%Ni-20%WP/AC was 11.9 umol/phosphide catalysts, cellulose was completely degraded in 30 which was higher than the 8.3 umol/g over the 20%WP/ACinEG was the main polyol product. For 20%WP/AC, the During cellulose conversion, the EG yield was remarkablyEG yield was 25. 4 mol%, with a hexitol yield of as low as 2.3 increased to 46.0 mol% over the nickel-modified tungstenmol%. This result is very close to that over a W2C/AC cataphosphide, which showed notable synergy in thest[8,9]. As mentioned above, a small amount of tungsten 2%Ni-20%WP/AC catalyst On the other hand, over a me-carbide was formed on 20%WP/AC, which may play an chanical mixture of 10%Ni/AC and 20%WP/AC, an EGimportant role in EG formation during cellulose conversion. yield of 34.1 mol% was obtained. Although this value wasTo exclude the influence of tungsten carbide, we used a higher than that over the individual catalysts, it was stillsilica-supported tungsten phosphide catalyst. Again, a good much lower than that from the 2%Ni-20%WP/AC catalystyield of EG was obtained on 20%WP/SiO2, in good agree- This result further demonstrated that a synergistic effectment with 20%WP/AC. The high selectivity for EG in cel- occurred when both Ni and w were present in one catalyst,ulose conversion should be attributed to the catalytic per- probably as neighbors to each other. On one hand, the tungformance of tungsten phosphide. As compared with nickel sten component in the catalysts degraded cellulose into smallphosphide, which we reported recently [12], the product molecules of C2 unsaturated species. On the other hand,selectivities were quite different even though both were tungsten catalyzed the hydrogenation of unsaturated moleetal phosphides. Cellulose was selectively transformed into cules into EG. Thus, with a proper amount of hydrogenatingsorbitol with a high yield of 48.4 mol% over nickel sites or using a novel preparation method to adjust the relaphosphide, while smaller molecule products, such as EG tive amounts of the two kinds of functions on the catalyst,were mainly formed over the tungsten phosphide catalyst By tungsten phosphide catalysts should give a better performcorrelating with our previous work on tungsten carbide and ance for cellulose conversion to EGmetallic tungsten catalysts [8-1l], we conclude that tungstenIn summary, tungsten phosphide catalysts showed goodphosphide functions as the active site for hydrogenation and activity for cellulose conversion to EG. Similar to tungstencarbide catalysts, a synergistic effect of duel catalytic sitesThe gas phase analysis showed that a small amount of co The addition of Ni into tungsten phosphide promoted cataand CO2 were produced but there were no methane or other lytic hydrogenation, and led to a remarkable increase of thealkanes formed during the reaction. The cellulose conversion EG yield to 46.0 mol%, The result is helpful for a betterwas 80%90% of total organic carbon. The reason for the understanding of cellulose conversion into EG over tung-10%-20% carbon loss after reaction is not clear yetsten-based catalysts, and provides less expensive catalystsThe reusability of the tungsten phosphide catalyst was for biomass conversionexamined with recycling tests. After three recycling runs, theH中国煤化工EG yield over 20%WP/AC decreased from 25.4 mol% to Full-text paper ar17.4mol%,indicatingthatslightdeactivationhadoccurredhttp://www.scCNMH722067