1、文章编号:摇 1007鄄8827(2019)06鄄0593鄄07氮杂炭催化剂催化 5鄄羟甲基糠醛选择性氧化制备 2,5鄄呋喃二甲醛滕摇 娜1,2,3,摇 李金龙1,2,3,摇 路博琼1,2,3,摇 王玉琪1,2,3,摇贾时宇1,2,3,摇 王英雄1,2,3,摇 侯相林1,2,3(1. 中国科学院山西煤炭化学研究所 山西省生物炼制工程技术研究中心, 山西 太原 030001;2. 中国科学院大学 材料与光电研究中心, 北京 100049;3. 中国科学院山西煤炭化学研究所 中国科学院炭材料重点实验室, 山西 太原 030001)摘摇 要:摇 利用氮杂炭材料作为催化剂,实现了 5鄄羟甲基糠醛(5鄄
2、HMF)选择性氧化制备 2,5鄄呋喃二甲醛(2,5鄄DFF)。 该氮杂炭催化剂通过壳聚糖热解制得,且壳聚糖是该催化剂的碳源和氮源,在热解过程中使用 K2CO3作为活化剂。 在不外加添加剂的情况下,该催化剂对 5鄄HMF 制备 2,5鄄DFF 展现出较高的催化活性。 在 120 益、7. 5 h 和 2. 0 MPa 氧气条件下,5鄄HMF 的转化率可达 95. 3%,2,5鄄DFF 的选择性可达 94. 6%。 氮杂炭催化剂表面的石墨型氮对分子氧的活化展现出高效的催化性能。同时,氧自由基的形成有利于 5鄄HMF 的氧化脱氢。 氮杂炭催化剂表面的石墨型氮是 5鄄HMF 选择性氧化制备 2,5鄄D
3、FF 的活性位点。 本研究为无金属催化 5鄄HMF 选择性氧化制备 2,5鄄DFF 提供了一条新思路。关键词: 摇 5鄄羟甲基糠醛;2,5鄄呋喃二甲醛;壳聚糖;氮杂炭;氧化脱氢中图分类号: 摇 TQ127. 1+1文献标识码: 摇 A基金项目:国家自然科学基金(U1710252,51703237);山西省应用基础研究项目(201701D221053).通讯作者:侯相林,研究员. E鄄mail: houxianglin sxicc. ac. cn;王玉琪,助理研究员. E鄄mail: wangyuqi sxicc. ac. cn作者简介:滕摇 娜,高级工程师. E鄄mail: tengna sx
4、icc. ac. cnThe selective aerobic oxidation of 5鄄hydroxymethylfurfuralto produce 2,5鄄diformylfuran usingnitrogen鄄doped porous carbons as catalystsTENG Na1,2,3,摇 LI Jin鄄long1,2,3,摇 LU Bo鄄qiong1,2,3,摇 WANG Yu鄄qi1,2,3,摇JIA Shi鄄yu1,2,2,摇 WANG Ying鄄xiong1,2,3,摇 HOU Xiang鄄lin1,2,3(1. Shanxi Engineering Res
5、earch Center of Biorefinery, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan030001, China;2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing100049, China;3. CAS Key Laboratory of Carbon Materials, Institute of Coal Che
6、mistry, Chinese Academy of Sciences, Taiyuan030001, China)Abstract: 摇 The selective aerobic oxidation of 5鄄hydroxymehtylfurfural (HMF) to synthesize 2,5鄄diformylfuran (DFF) using ni鄄trogen鄄doped porous carbons as catalysts was achieved. The N鄄doped carbon materials were prepared by pyrolysis of chit
7、osan withK2CO3as an activator at 600 to 900 益. The N鄄doped porous carbon activated at 700 益 showed the highest catalytic activity in theconversion from HMF to DFF without any co鄄catalyst, i. e. , the 95. 3% HMF conversion and 94. 6% selectivity of DFF under opti鄄mum reaction conditions (120 益, 7. 5
8、h and 2. 0 MPa O2). According to the XPS results graphitic nitrogen on the surface of thecatalysts played a critical role in the activation of O2to form oxygen radicals that facilitated the oxidative dehydrogenation of HMF.Key words:摇 5鄄Hydroxymethylfurfural; 2,5鄄Diformylfuran; Chitosan; Nitrogen鄄do
9、ped carbon; Oxidative dehydrogenationReceived date: 2019鄄11鄄10;摇 Revised date: 2019鄄12鄄05Foundation item: National Natural Science Foundation of China (U1710252, 51703237); Applied Fundamental Research Project ofShanxi Province (201701D221053).Corresponding authors: HOU Xiang鄄lin, Professor. E鄄mail:
10、 houxianglin sxicc. ac. cn; WANG Yu鄄qi, Assistant Research Fellow.E鄄mail: wangyuqi sxicc. ac. cnAuthor introduction: TENG Na, Senior Engineer. E鄄mail: tengna sxicc. ac. cnEnglish edition available online ScienceDirect (http:蛐蛐www. sciencedirect. com蛐science蛐journal蛐18725805).Supplementary data assoc
11、iated with this article can be found in the online version.DOI: 10. 1016/ S1872鄄5805(19)60034鄄X摇第 34 卷摇 第 6 期2019 年 12 月新摇 型摇 炭摇 材摇 料NEW CARBON MATERIALSVol. 34摇 No. 6Dec. 2019摇1摇 IntroductionDue to depletion of fossil reserves and environ鄄ment problems, the catalytic conversion of biomass toobtain
12、high value鄄added chemicals and fuel attractedgrowingattention1鄄3.5鄄Hydroxymethylfurfural(HMF) was one of the most important platform com鄄pounds derived from acidic hydrolysis of carbohy鄄drates4鄄6. As the most important intermediate, HMFcan be transformed into various useful chemicals,such as 2,5鄄dif
13、ormylfuran (DFF), 2,5鄄dimethylfuran(DMF), 2,5鄄furandicarboxylic acid (FDCA), 5鄄ethoxymethylfurfural ( EMF) and maleic anhydride(MA)7鄄11. DFF, which can be achieved from theselective oxidation of HMF, was widely applied tosynthesize heterocyclic ligands, anti鄄fungal agents,pharmaceuticals, organic co
14、nductors and so on12,13.Generally, the aerobic oxidation of HMF to pro鄄duce DFF was catalyzed by transition metals such asRu, Cu, V, Mn/ Co and Cu/ V using oxygen as theterminal oxidant14鄄18. The metal鄄based catalysts canprovide an excellent DFF yield in the oxidation ofHMF. However, the metals were
15、 expensive, toxicand easily losing during the reaction. Therefore, it isnecessary to develop an efficient metal鄄free heteroge鄄neous catalyst for the oxidation of HMF to prepareDFF.Nitrogen鄄doped carbon was a versatile materialwhich can be used for oxidation reaction and organicsynthesis, and acted a
16、s an electrode material, absorb鄄ent material and so on19鄄24. Nitrogen鄄doped carbonmaterials as catalysts were utilized for the aerobic oxi鄄dation in recent years.For example, Fujita et al.demonstrated that N鄄doped activated carbon can beapplied for the aerobic oxidation of xanthene to xan鄄thone25.An
17、d nitrogen鄄doped graphene nanosheetswere investigated in the aerobic oxidation of primaryalcohols to acquire corresponding aldehydes23. Ni鄄trogen鄄doped carbon materials derived from chitosanwere employed in producing FDCA from the oxida鄄tion of HMF under alkaline conditions26. The oxida鄄tion of benz
18、ylic alcohol, cinnamyl alcohol and HMFto acquire corresponding aldehydes was catalyzed bythe nitrogen鄄doped activated carbon. For selective ox鄄idation of HMF, a 24% conversion of HMF wasachieved with a 93% selectivity of DFF for 15 h27.And Zhang et al. reported that HNO3鄄promoted oxi鄄dation of HMF t
19、o prepare DFF was smoothly conduc鄄ted with nitrogen鄄doped carbon materials as the cata鄄lysts, which was prepared by pyrolysis of chitosanand urea28. In our group爷s previous work, grapheneoxide and nitrogen鄄doped graphene presented a highcatalytic activity for the selective oxidation of HMFusing2, 2
20、爷, 6, 6 爷鄄tetramethylpiperidine鄄1鄄oxyl(TEMPO) as a co鄄catalyst29,30. However, the prep鄄aration procedure of graphene oxide and nitrogen鄄doped graphene was complex and difficult, and thehomogeneous additives, such as TEMPO and HNO3,cannot be recovered and reused.Chitosan, as a natural nitrogen鄄contai
21、ning mac鄄romolecule, was widely present in marine living re鄄sources31. Nitrogen鄄doped carbon materials can beprepared from chitosan by in鄄situ nitrogen dopingwithout the addition of nitrogen precursors. The ob鄄tained nitrogen鄄doped carbon materials were exploredin the selective aerobic oxidation of
22、HMF to produceDFF. And no other additives were added in the reac鄄tion system. The results of XPS show that three typesof nitrogen species were present on the surfaces, in鄄cluding pyridinic N, pyrrolic N and graphitic N. Thegraphitic nitrogen is essential for the formation of ac鄄tivity centers in the
23、 oxidation reaction on the basis ofthe good linear correlation between the initial reactionrate and graphitic N/ C atomic ratio. The strategy pro鄄vides a promising way for the aerobic oxidation ofHMF to produce DFF.2摇 Experimental2. 1摇 MaterialsHMF, DFF and 5鄄formyl鄄2鄄furancarboxylic acid(FFCA) were
24、 purchased from DEMO Medical Tech.Co. , Ltd. Other chemicals were supplied from Sino鄄pharm Chemical Reagent Co. , Ltd. All the chemicalswere analytical grade and used without further purifi鄄cation.2. 2摇Preparation of nitrogen鄄doped carbon mate鄄rialsNitrogen鄄doped carbon materials were preparedfrom c
25、hitosan by pyrolysis, and the general procedureof preparation procedure was as follows32. The chi鄄tosan was coked at 400 益 for 3 h in N2atmosphere.After coking, the black bio鄄char was gained. Then,the bio鄄char powder and the activator K2CO3weremixed at a mass ratio of 1 颐2. The pyrolysis was per鄄for
26、med at a certain temperature (600, 700, 800 or900 益) for 2 h in N2atmosphere.The nitrogen鄄doped carbon materials were achieved after cooling toroomtemperature.Theobtainedmaterialswerewashed by a 1 mol/ L hydrochloric acid solution anddeionized water consecutively.Then, the materialswere dried in an
27、oven at 80 益 for 12 h. The nitro鄄gen鄄doped carbon materials derived from chitosan u鄄sing K2CO3as the activator were defined as Ch鄄K鄄T,where Ch was chitosan鄄based carbon materials, K wasthe activator K2CO3and T was the carbonization tem鄄495摇新摇 型摇 炭摇 材摇 料第 34 卷perature in the second step. To testify t
28、he effective鄄ness of nitrogen, the nitrogen鄄free bio鄄carbon materialwas gained from cellulose. The carbon material de鄄rived from cellulose was defined as Ce鄄K鄄T. To ex鄄plore the effect of the activator, the chitosan鄄basedcarbon material was prepared in the absence of the ac鄄tivator during pyrolysis,
29、 and it was defined as Ch鄄T.2. 3 摇Characterization of nitrogen鄄doped carbonmaterialsThe specific surface area was calculated using theBrunauer鄄Emmett鄄Teller (BET) equation from nitro鄄gen adsorption isotherms at 77 K using an AU鄄TOSORB鄄1鄄MP Tristar II 3020 apparatus. X鄄ray dif鄄fraction (XRD) patterns
30、 were conducted on a BrukerD8鄄ADVANCE A25 diffractometer using Cu鄄K琢 radi鄄ation. The samples were scanned in the range of 5 鄄90毅 at a scanning rate of 2 毅/ min. Transmission elec鄄tron microscopy (TEM, Tecnai G2 F20 S鄄Twin) wasused to observe the microstructure of samples. X鄄rayphotoelectron spectros
31、copy was performed on a specsspectrometer (XPS, AXIS ULTRA DLD) using AlK琢 X鄄ray source (1 486. 6 eV). Nuclear MagneticResonance (NMR) spectra of the separated productswere collected on a Bruker AV鄄 III 400 MHz NMRspectrometer.2. 4摇 Catalytic oxidation of HMFThe aerobic oxidation of HMF was performe
32、d ina stainless steel autoclave (100 mL) equipped with amagnetic stirrer and an automatic temperature controlapparatus. In a typical reaction, 1. 0 mmol of HMF,100 mg of nitrogen鄄doped carbon materials and 30 mLof acetonitrile were added to the reactor. The reactorwas sealed and filled by oxygen unt
33、il the pressurereached 2. 0 MPa. The reaction was conducted at adesired reaction temperature. After the reaction, thereaction mixture was diluted by deionized water andfiltered by a 0. 45 滋m syringe filter.The HMF conversion and DFF yield were deter鄄mined by a high performance liquid chromatograph(
34、HPLC, Shimadzu, LC鄄10AT ).The chromato鄄graphic column was a reversed鄄phased C18 column(200 mm 伊 4. 6 mm) and the detector was a ultravio鄄let鄄visible detector (detection wavelength, 280 nm).The mobile phase was consisted of 69. 9 wt% deion鄄ized water, 30 wt% acetonitrile and 0. 1 wt% aceticacid and t
35、he flow velocity was 0. 3 mL min鄄1. Thecolumn temperature was kept at 35 益.The HMFconversion, DFF yield and FFCA yield were calculat鄄ed by an external standard method.3摇 Results and discussion3. 1 摇Characterization of nitrogen鄄doped carbonmaterialsThe morphologies and structures of obtained ni鄄troge
36、n鄄doped carbon materials were observed by TEM(Fig. S1). It can be seen that the morphology of Ch鄄K鄄700 was laminar and amorphous. The XRD resultsalso represented that there were two diffraction peaksat around 23毅 and 43毅 which demonstrated Ch鄄K鄄700was amorphous (Fig. S2). The pore textural proper鄄ti
37、es of nitrogen鄄doped carbon materials were moni鄄tored by nitrogen adsorption (Table 1). The SBET, Vpand average pore size of catalysts increased with thepyrolysis temperature from 600 to 900 益. However,the Smicroand Vmicroof catalysts reached the maxima of1 901 m2 g鄄1and 0. 74 cm3 g鄄1at the pyrolysi
38、s temper鄄ature of 800 益. The results revealed that the pyroly鄄sis temperature determines the formation of pores.The pyrolysis temperature of 800 益 was beneficial tothe formation of micropores. When the temperatureexceeded 800 益, a part of the micropores was de鄄stroyed due to the excessive etching.Ta
39、ble 1摇 Pore textural properties of nitrogen鄄doped carbon materials by nitrogen adsorption.EntrySamplesSBET/ m2 g鄄1Smicro/ m2 g鄄1Vp/ cm3 g鄄1Vmicro/ cm3 g鄄1Average pore size/ nm1Ch鄄K鄄6006375890.250.231.592Ch鄄K鄄700156014380.630.561.603Ch鄄K鄄800210119010.850.741.614Ch鄄K鄄90024757891.310.342.12摇摇The chemic
40、al compositions of the catalyst sur鄄faces were detected by XPS (Fig. 1). The character鄄istic peaks of C 1s, N 1s and O 1s were observed at285, 401 and 532 eV (Fig. 1a), respectively. Thechemical states of N and O of the catalyst surfaceswere further investigated by deconvolution of XPSpeaks (Fig. 1b
41、 and c). The possible chemical struc鄄ture of nitrogen鄄doped carbon materials was proposed(Fig. 1d). It can be seen that the catalyst surfacecontains three types of N species including pyridinic N(N1), pyrrolic N (N2) and graphitic N (N3). Thepeaks at 398. 1, 399. 4 and 401. 7 eV were attributedto N1
42、, N2and N3, respectively (Figure 1b). Thecontents of C, N and O were calculated by XPS re鄄sults (Table S1). It can be seen that the N content ofcatalysts decreased from 6. 4 at% to 2. 0 at% with the595第 6 期TENG Na et al: The selective aerobic oxidation of 5鄄hydroxymethylfurfural 摇pyrolysis temperatu
43、re from 600 to 900 益. It is note鄄worthy that the N3content reached the maximumwhen the pyrolysis temperature was 700 益. The Ospecies of catalyst surface was also identified by XPS(Fig. 1c). The peak at 530. 6 eV was attributed to詤詤CO , the peak at 532. 2 eV was assigned to theadsorbed oxygen and tha
44、t at 533. 3 eV was ascribed toCOH or COC.Fig. 1摇 (a) XPS patterns of the nitrogen鄄doped carbon materials obtained at different pyrolysis temperatures,(b) High resolution N 1s XPS spectra of samples, (c) High resolution O 1s XPS spectra of samples and(d) An illustration of nitrogen species of the nit
45、rogen鄄doped carbon materials.3. 2摇 Aerobic oxidation of HMF to DFFThe aerobic oxidation of HMF was catalyzed bythe nitrogen鄄doped carbon materials (Table 2). TheHMF conversion was only 1. 3% in the absent of thecatalyst ( Table 2, entry 1).When the nitrogen鄄doped carbon materials were added, the HMF
46、 conver鄄sion and DFF yield were dramatically increased (Ta鄄ble 2, entry 2鄄5). The Ch鄄K鄄700 presented the bestcatalytic performance among the nitrogen鄄doped car鄄bon materials prepared at 600, 800 and 900 益. TheHMF conversion was 60. 6%, and the DFF yield was59. 6% (Table 2, entry 3). The results show
47、ed thatthe pyrolysis temperature should be determining factorfor the catalytic performance of nitrogen鄄doped car鄄bons in the oxidation reaction of HMF. For the con鄄trol experiments without the activator and but with ni鄄trogen species, the HMF conversion was only 5. 0%using Ch鄄700 as a catalyst, indi
48、cating that the activa鄄tor played a crucial role for the catalytic activity (Ta鄄ble 2, entry 6). The HMF conversion decreased to10. 2% using Ce鄄K鄄700 as the catalyst, suggestingthat nitrogen doping for catalysts were indispensablein the oxidation reaction (Table 2, entry 7). The Ch鄄K鄄700 was selecte
49、d as the catalyst by comparison. Toverify the effect of oxygen, the reaction was carriedout in N2atmosphere. It was found that the HMFconversion dramatically decreased to 7. 0% (Table 2,entry 8).The result demonstrates that the oxygenmolecule participated in the oxidation reaction. Then,benzoquinone
50、 as a radical scavenger was added duringthe aerobic oxidation (Table 2, entry 9). The HMFconversion decreased to 31. 7% from 60. 6%, whichrevealed that the radical species were involved in thepreparation of DFF from HMF.The aerobic oxidation of HMF catalyzed by Ch鄄K鄄700 was optimized (Fig. 2). The e
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