钯掺杂α-MnO_2无溶剂下催化氧化苯甲醇的性能
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摘要
通过共沉淀和原位煅烧转化方法,将Pd掺杂δ-MnO_2前驱体煅烧后制备得到Pd掺杂α-MnO_2纳米棒催化材料.通过氮气物理吸附、X射线衍射、透射电子显微镜、扫描电子显微镜、热重分析、X射线光电子能谱等技术对催化材料进行了表征.扫描电镜和透射电镜结果显示,α-MnO_2纳米棒表面没有明显的Pd纳米颗粒,表明Pd可能掺杂到α-MnO_2晶格中.纯α--MnO_2的还原温度在390℃左右,但Pd掺杂可以极大地促进α-MnO_2还原,还原温度可低至约200℃左右.研究了所制备催化剂在无溶剂条件下对于以分子氧为氧化剂选择性催化氧化苯甲醇为苯甲醛的催化性能.结果表明:在无溶剂及用纯氧气为氧化剂条件下,Pd掺杂α-MnO_2纳米棒对苯甲醇氧化显示出增强的催化活性;所掺杂的氧化态Pd物质可增强催化材料中的氧迁移率;在这些Pd掺杂α-MnO_2催化材料中,当以Pd(3%,质量分数)-MnO_2为催化剂时,在110℃反应4 h后,苯甲醇的转化率为39%,远高于同条件下以纯α-MnO_2为催化剂时18. 3%的苯甲醇转化率.
Liquid-phase selective oxidation of benzyl alcohol to benzaldehyde is one of the most important processes in both laboratory and chemical industry processes due to the remarkable values of benzaldehyde in the production of flavours,fragrances,and biologically active compounds. In the traditional processes for selective oxidation of benzyl alcohol using a stoichiometric or excessive amount of toxic and expensive inorganic oxidants,such as ammonium permanganate in aqueous acidic medium,a large amount of toxic waste is produced. A few studies on the benzyl alcohol-to-benzaldehyde oxidation by environmentally clean oxidants( O_2 or H_2O_2) in the presence of organic solvents( e. g.,toluene,p-xylene,and trifuorotoluene) have been reported; however,the usage of organic solvent is neither economical nor environmental friendly. Even though the solvent-free oxidation of benzyl alcohol to benzaldehyde using tert-butylhydroperoxide( TBHP) as oxidant has been reported,the co-product of tert-butanol from the consumption of TBHP will be left in the reaction solution,necessitating further separation. Therefore,various heterogeneous catalysts have been developed for solvent-free selective oxidation of benzyl alcohol using flowing air or oxygen; however,in most of these systems,the reaction temperature is still high( > 130 ℃) and/or conversion/selectivity is still low. Thus,the development of efficient heterogeneous catalysts for the solvent-free se-lective oxidation of benzyl alcohol with high selectivity and yield using molecular oxygen from air as the oxidant at low temperature is needed. In this study,Pd-doped α-MnO_2 nanorods were prepared from Pd-doped δ-MnO_2 precursors via a co-precipitation and in situ calcination transformation method. These catalysts were extensively characterized by various techniques,such as N_2 adsorption,X-ray diffraction( XRD),transmission electron microscopy( TEM),scanning electron microscopy( SEM),thermogravimetric analysis( TGA),and X-ray photoelectron spectroscopy( XPS). The SEM and TEM results indicate that there are no obvious Pd nanoparticles on the surface of α-MnO_2 nanorods,signifying the possible doping of Pd into the lattice of α-MnO_2. The reduction temperature of pureα-MnO_2 is around 390 ℃,while the doped Pd could greatly promote α-MnO_2 reduction to lower temperatures at around 200 ℃. The applications of Pd-doped α-MnO_2 nanorods as catalysts for selective aerobic oxidation of benzyl alcohol to benzaldehyde under solventfree conditions with molecular oxygen were investigated. As compared with pure α-MnO_2,the Pd-doped α-MnO_2 nanorods show enhanced catalytic activity for selective oxidation of benzyl alcohol under solvent-free conditions with O_2,which can be attributed to the beneficial presence of oxidized palladium species and enhanced oxygen mobility resulting from the doping Pd species. In these Pddoped α-MnO_2 nanorods,when Pd( 3%)-MnO_2 was used as catalyst,a 39% conversion of benzyl alcohol was achieved. It is much higher than the 18. 3% conversion when pure α-MnO_2 used as catalyst at 110 ℃ and reaction time of 4 h.
Liquid-phase selective oxidation of benzyl alcohol to benzaldehyde is one of the most important processes in both laboratory and chemical industry processes due to the remarkable values of benzaldehyde in the production of flavours,fragrances,and biologically active compounds. In the traditional processes for selective oxidation of benzyl alcohol using a stoichiometric or excessive amount of toxic and expensive inorganic oxidants,such as ammonium permanganate in aqueous acidic medium,a large amount of toxic waste is produced. A few studies on the benzyl alcohol-to-benzaldehyde oxidation by environmentally clean oxidants( O_2 or H_2O_2) in the presence of organic solvents( e. g.,toluene,p-xylene,and trifuorotoluene) have been reported; however,the usage of organic solvent is neither economical nor environmental friendly. Even though the solvent-free oxidation of benzyl alcohol to benzaldehyde using tert-butylhydroperoxide( TBHP) as oxidant has been reported,the co-product of tert-butanol from the consumption of TBHP will be left in the reaction solution,necessitating further separation. Therefore,various heterogeneous catalysts have been developed for solvent-free selective oxidation of benzyl alcohol using flowing air or oxygen; however,in most of these systems,the reaction temperature is still high( > 130 ℃) and/or conversion/selectivity is still low. Thus,the development of efficient heterogeneous catalysts for the solvent-free se-lective oxidation of benzyl alcohol with high selectivity and yield using molecular oxygen from air as the oxidant at low temperature is needed. In this study,Pd-doped α-MnO_2 nanorods were prepared from Pd-doped δ-MnO_2 precursors via a co-precipitation and in situ calcination transformation method. These catalysts were extensively characterized by various techniques,such as N_2 adsorption,X-ray diffraction( XRD),transmission electron microscopy( TEM),scanning electron microscopy( SEM),thermogravimetric analysis( TGA),and X-ray photoelectron spectroscopy( XPS). The SEM and TEM results indicate that there are no obvious Pd nanoparticles on the surface of α-MnO_2 nanorods,signifying the possible doping of Pd into the lattice of α-MnO_2. The reduction temperature of pureα-MnO_2 is around 390 ℃,while the doped Pd could greatly promote α-MnO_2 reduction to lower temperatures at around 200 ℃. The applications of Pd-doped α-MnO_2 nanorods as catalysts for selective aerobic oxidation of benzyl alcohol to benzaldehyde under solventfree conditions with molecular oxygen were investigated. As compared with pure α-MnO_2,the Pd-doped α-MnO_2 nanorods show enhanced catalytic activity for selective oxidation of benzyl alcohol under solvent-free conditions with O_2,which can be attributed to the beneficial presence of oxidized palladium species and enhanced oxygen mobility resulting from the doping Pd species. In these Pddoped α-MnO_2 nanorods,when Pd( 3%)-MnO_2 was used as catalyst,a 39% conversion of benzyl alcohol was achieved. It is much higher than the 18. 3% conversion when pure α-MnO_2 used as catalyst at 110 ℃ and reaction time of 4 h.
引文
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[20] Ousmane M,Perrussel G,Yan Z,et al. Highly selective direct amination of primary alcohols over a Pd/K-OMS-2 catalyst. J Catal,2014,309:439
[21] Hegde M S,Bera P. Noble metal ion substituted CeO2catalysts:Electronic interaction between noble metal ions and CeO2lattice.Catal Today,2015,253:40
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[23] Gentry S J,Hurst N W,Jones A. Study of the promoting influence of transition metals on the reduction of cupric oxide by temperature programmed reduction. J Chem Soc,Faraday Trans 1,1981,77(3):603
[24] Gulyaev R V,Kardash T Y,Malykhin S E,et al. The local structure of PdxCe1-xO2-x-δsolid solutions. Phys Chem Chem Phys,2014,16(26):13523
[25] Dupin J C,Gonbeau D,Vinatier P,et al. Systematic XPS studies of metal oxides,hydroxides and peroxides. Phys Chem Chem Phys,2000,2(6):1319
[26] Makwana V D,Son Y C,Howell A R,et al. The role of lattice oxygen in selective benzyl alcohol oxidation using OMS-2 catalyst:a kinetic and isotope-labeling study. J Catal,2002,210(1):46
[27] Dimitratos N,Lopez-Sanchez J A,Morgan D,et al. Solvent-free oxidation of benzyl alcohol using Au-Pd catalysts prepared by sol immobilization. Phys Chem Chem Phys,2009,11(25):5142
[28] Zhang Y,Qi X J,Cui X J,et al. Palladium catalyzed N-alkylation of amines with alcohols. Tetrahedron Lett,2011,52(12):1334
[2] Kotai L,Kazinczy B,Keszler A,et al. Three reagents in one:ammonium permanganate in the oxidation of benzyl alcohol. Z Naturforsch B,2001,56(8):823
[3] Wu Z Y,Huang X B,Zheng H Y,et al. Aromatic heterocyclegrafted NH2-MIL-125(Ti)via conjugated linker with enhanced photocatalytic activity for selective oxidation of alcohols under visible light. Appl Catal B-Environ,2018,224:479
[4] Li H,Qin F,Yang Z P,et al. New reaction pathway induced by plasmon for selective benzyl alcohol oxidation on BiOCl possessing oxygen vacancies. J Am Chem Soc,2017,139(9):3513
[5] Mandal S,Chowdhury B. Solvent-free benzyl alcohol oxidation reaction over Sm-CeO2supported gold nanoparticle using tert-butyl hydroperoxide(TBHP)as an oxidant. Nat Resour Eng,2016,1(2):43
[6] Renuka M K,Gayathri V. A polymer supported Cu(II)catalyst for oxidative amidation of benzyl alcohol and substituted amines in TBHP/H2O. Catal Commun,2018,104:71
[7] Hong Y L,Jiang X L,Huang J L,et al. Biosynthesized bimetallic Au-Pd nanoparticles supported on Ti O2for solvent-free oxidation of benzyl alcohol. ACS Sustainable Chem Eng,2014,2(7):1752
[8] Galvanin F,Sankar M,Cattaneo S,et al. On the development of kinetic models for solvent-free benzyl alcohol oxidation over a goldpalladium catalyst. Chem Eng J,2018,342:196
[9] Li T B,Liu F,Tang Y,et al. Maximizing the number of interfacial sites in single-atom catalysts for the highly selective,solventfree oxidation of primary alcohols. Angew Chem Int Ed,2018,57(26):7795
[10] Weerachawanasak P,Hutchings G J,Edwards J K,et al. Surface functionalized Ti O2supported Pd catalysts for solvent-free selective oxidation of benzyl alcohol. Catal Today,2015,250:218
[11] Xin P Y,Li J,Xiong Y,et al. Revealing the active species for aerobic alcohol oxidation by using uniform supported palladium catalysts. Angew Chem Int Ed,2018,57(17):4642
[12] Enache D I,Edwards J K,Landon P,et al. Solvent-free oxidation of primary alcohols to aldehydes using Au--Pd/Ti O2catalysts. Science,2006,311(5759):362
[13] Zhu Y,Zhang S R,Shan J J,et al. In situ surface chemistries and catalytic performances of ceria doped with palladium,platinum,and rhodium in methane partial oxidation for the production of syngas. ACS Catal,2013,3(11):2627
[14] Jin Z,Nackashi D,Lu W,et al. Decoration,migration,and aggregation of palladium nanoparticles on graphene sheets. Chem Mater,2010,22(20):5695
[15] Biswas S,Dutta B,Mullick K,et al. Aerobic oxidation of amines to imines by cesium-promoted mesoporous manganese oxide. ACS Catal,2015,5(7):4394
[16] Dutta B,Biswas S,Sharma V,et al. Mesoporous manganese oxide catalyzed aerobic oxidative coupling of anilines to aromatic azo compounds. Angew Chem Int Ed,2016,55(6):2171
[17] Li Z,Wang L,Yun L,et al. Activity and antitoxic properties of Cr--Mn Ox/Ti O2-Zr O2for low-temperature selective catalytic reduction of NO. Chin J Eng,2015,37(8):1049(李哲,汪莉,贠丽,等. Cr-MnOx/Ti O2-Zr O2低温选择催化还原NO的活性及抗毒性能.工程科学学报,2015,37(8):1049)
[18] Alhumaimess M,Lin Z J,He Q,et al. Oxidation of benzyl alcohol and carbon monoxide using gold nanoparticles supported on MnO2nanowire microspheres. Chem Eur J,2014,20(6):1701
[19] Ragupathy P,Park D H,Campet G,et al. Remarkable capacity retention of nanostructured manganese oxide upon cycling as an electrode material for supercapacitor. J Phys Chem C,2009,113(15):6303
[20] Ousmane M,Perrussel G,Yan Z,et al. Highly selective direct amination of primary alcohols over a Pd/K-OMS-2 catalyst. J Catal,2014,309:439
[21] Hegde M S,Bera P. Noble metal ion substituted CeO2catalysts:Electronic interaction between noble metal ions and CeO2lattice.Catal Today,2015,253:40
[22] Hensley A J R,Hong Y C,Zhang R Q,et al. Enhanced Fe2O3reducibility via surface modification with Pd:characterizing the synergy within Pd/Fe catalysts for hydrodeoxygenation reactions.ACS Catal,2014,4(10):3381
[23] Gentry S J,Hurst N W,Jones A. Study of the promoting influence of transition metals on the reduction of cupric oxide by temperature programmed reduction. J Chem Soc,Faraday Trans 1,1981,77(3):603
[24] Gulyaev R V,Kardash T Y,Malykhin S E,et al. The local structure of PdxCe1-xO2-x-δsolid solutions. Phys Chem Chem Phys,2014,16(26):13523
[25] Dupin J C,Gonbeau D,Vinatier P,et al. Systematic XPS studies of metal oxides,hydroxides and peroxides. Phys Chem Chem Phys,2000,2(6):1319
[26] Makwana V D,Son Y C,Howell A R,et al. The role of lattice oxygen in selective benzyl alcohol oxidation using OMS-2 catalyst:a kinetic and isotope-labeling study. J Catal,2002,210(1):46
[27] Dimitratos N,Lopez-Sanchez J A,Morgan D,et al. Solvent-free oxidation of benzyl alcohol using Au-Pd catalysts prepared by sol immobilization. Phys Chem Chem Phys,2009,11(25):5142
[28] Zhang Y,Qi X J,Cui X J,et al. Palladium catalyzed N-alkylation of amines with alcohols. Tetrahedron Lett,2011,52(12):1334
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