Ni/HZSM-5催化剂的结构及其催化山梨醇水相加氢合成烷烃性能

采用浸渍法制备了Ni/HZSM-5双功能催化剂,考察了焙烧温度对催化剂结构及其催化山梨醇水相加氢合成C5～C6烷烃性能的影响.结果表明,在金属中心和酸性载体的协同作用下,通过山梨醇中C-O键加氢和异构化高选择性合成了C5～C6烷烃.经500°C焙烧的Ni/HZSM-5催化剂上山梨醇水相加氢的活性最高,山梨醇转化率为62.0%,戊烷和己烷的总选择性为76.4%,其中异己烷选择性达45.4%.对催化剂进行N2物理吸附、X射线衍射、NH3程序升温脱附和H2程序升温还原等表征后发现,经500°C焙烧催化剂的有效比表面积和孔体积均明显增大,HZSM-5负载的硝酸镍分解成较小晶粒的NiO,表面酸量适中,且Ni物种与载体相互作用较强,较易被H2还原,Ni还原度达100%.这是其催化活性最高的原因.     

Ni/HZSM-5的结构及催化木糖醇水相加氢合成液体烷烃的性能研究

采用浸渍法制备了Ni/HZSM-5双功能催化剂,采用BET、XRD、NH3-TPD、H2-TPR、FTIR和TG等方法表征了催化剂比表面、孔结构、酸性、还原能力及骨架结构等信息,研究了其催化木糖醇水相加氢合成液体烷烃的性能及催化剂失活的原因。结果表明,在优化的金属中心/酸中心的协同作用下,木糖醇可通过水相加氢高选择性地合成C5-C6烷烃;过高的金属中心或酸中心均会导致C-C键断裂形成轻质烷烃,以2%Ni/HZSM-5催化剂上木糖醇水相加氢活性最高,木糖醇C转化率为94%液体烷烃总收率可达90%,这与其具有较大的比表面积、合适的孔径分布、较多的金属活性中心、适中的酸量和强酸量有关。催化剂6次重复使用后活性明显降低,其骨架部分脱铝和表面积碳是其失活的主要原因。     

Enhanced Stability of Mo-Promoted Zn/HZSM-5 Catalyst for Methanol to Aromatics

A Mo-promoted Zn/HZSM-5 catalyst was prepared by isometric impregnation method (IM). The physicochemical properties of catalysts were characterized by X-ray diffraction, registration of N₂ adsorption-desorption isotherms, transmission electron microscopy, NH₃ temperature-programmed desorption and IR spectroscopic study of pyridine adsorption. The results show that by doping zeolite with Mo species it is possible to tune the microstructures, acidity and crystallinity of the catalyst. Additionally, it was found that the 1%Mo(IM)–5%Zn(IE)/HZSM-5 catalyst had a high catalytic activity and stability for methanol to aromatics (MTA) reaction. The yield of aromatics reached 77.3% at 450°C and TOS = 3 h. When the TOS = 98 h, the yield of total aromatics remains at a 60.4% level. The lifetime of catalysts was influenced by the synergetic effect of Brønsted and Lewis acid sites, so the modification with Mo may bring an opportunity to prolong the lifetime of Zn/HZSM-5 catalyst in the MTA reaction. The metal components are sintered and lost in continuous reaction-regeneration cycles. Accordingly, the activity of deactivated catalyst cannot be completely restored to the initial level.     

康熙《皇城宫殿衙署图》解读(下)*

以尿素为沉淀剂,采用负压沉积沉淀法将Au负载于不同载体,分别制备了Au/HZSM-5、 Au/SiO_2及Au/Al_2O_3催化剂.采用X射线粉末衍射、透射电镜、 NH_3-程序升温脱附、红外羟基和原位吸附吡啶红外羟基等技术对催化剂进行了表征,探究了Au对不同载体的作用,并用脉冲微反装置评价了催化剂对正丁烷脱氢反应的性能.结果表明,相较于其他载金催化剂, Au/HZSM-5酸性较强, Au与HZSM-5相互作用后会形成Si-O(H)-Au基团,该活性相对正丁烷脱氢起到一定的促进作用.     

钾改性对Au/ZSM-5催化剂上正丁烷裂解性能的影响

采用负压沉积沉淀法制备了负载型Au/HZSM-5催化剂,采用X射线衍射（XRD）、透射电镜（TEM）、Ｘ射线光电子能谱（XPS）、NH3-TPD、紫外可见漫反射（UV-vis）等技术对催化剂进行了表征分析,并考察了催化剂对正丁烷裂解性能的影响。结果表明,Au金属成功负载到HZSM-5催化剂上,并且金颗粒的尺寸受负载量的影响,其中1.0%Au/HZSM-5催化剂中的金颗粒粒径最小,约为5～10nm。钾离子作为一种碱性离子可以调节载体酸性,随着K离子的引入xK-Au/HZSM-5催化剂的酸性逐渐降低,使Au0的电子结合能更高。相对于HZSM-5,2.0Au/HZSM-5催化剂对于正丁烷的转化率从13.1%提升到了37.5%,对丙烯的选择性从17.2%提升到了52.5%。随着K离子的引入,催化剂对于丁烯以及异丁烷的选择性有所提高,当K离子负荷为0.08%时,对丁烯的选择性从3.8%提高到36.9%,负荷为0.1%时,对异丁烷的选择性由2.8%提升到51.8%。但原料转化率低于2.0Au/HZSM-5,这可能与K的加入降低催化剂酸改性有关。此外通过研究Au/HZSM-5用K+修饰得知Au+离子是Au/HZSM-5催化剂转化正丁烷主要活性中心。     

Conversion of Polysaccharides to Sugar Alcohols: A Modeling Approach Based on Oligosaccharides

We extend our former kinetic and experimental study of hydrogenolysis of di‐ and trisaccharides using Ru/C in combination with a molecular acid as a catalyst system, to longer oligosaccharides up to heptasaccharide. The extended kinetics, despite the considerably more complex reaction network, reconfirms our previous hypothesis that reactions of oligosaccharides proceed through two competing reaction pathways, namely hydrolysis of oligosaccharides and their hydrogenation to a reduced form. This challenges the widely accepted supposition that conversion of polysaccharides to sorbitol passes consecutively through hydrolysis to monosaccharides followed by hydrogenation to sorbitol. This works also sets forth the hypothesis that hydrogenation of long‐chain oligosaccharides increases the rate of hydrolysis to a considerable extent and presents a significant alternative pathway in sorbitol formation.     

在Ni/HZSM-5催化剂上低温水蒸汽重整生物油制氢

We investigated high catalytic activity of Ni/HZSM-5 catalysts synthesized by the impregna-tion method, which was successfully applied for low-temperature steam reforming of bio-oil. The influences of the catalyst composition, reforming temperature and the molar ratio of steam to carbon fed on the stream reforming process of bio-oil over the Ni/HZSM-5 catalysts were investigated in the reforming reactor. The promoting effects of current passing through the catalyst on the bio-oil reforming were also studied using the electrochemical catalytic re-forming approach. By comparing Ni/HZSM-5 with commonly used Ni/Al₂O₃ catalysts, the Ni₂₀/ZSM catalyst with Ni-loading content of about 20% on the HZSM-5 support showed the highest catalytic activity. Even at 450 oC, the hydrogen yield of about 90% with a near complete conversion of bio-oil was obtained using the Ni₂₀/ZSM catalyst. It was found that the performance of the bio-oil reforming was remarkably enhanced by the HZSM-5 supporter and the current through the catalyst. The features of the Ni/HZSM-5 catalysts were also investigated via X-ray diffraction, inductively coupled plasma and atomic emission spectroscopy, hydrogen temperature-programmed reduction, and Brunauer-Emmett-Teller methods.     

DEHYDROGENATION AND AROMATIZATION OF METHANE IN THE ABSENCE OF OXYGEN OVER DOPED Mo/HZSM-5 CATALYSTS

研究了在Ｍｏ／ＨＺＳＭ－５催化剂上添加助剂以及不同的反应预处理温度对甲烷无氧脱氢芳构化反应的影响。实验结果表明，由于第二组分的添加，Ｍｏ／ＨＺＳＭ－５催化剂的活性和选择性都得到了较大程度的改善。预处理温度是影响催化剂反应性能的关键因素。Ｍｏ－Ｒｕ／ＨＺＳＭ－５催化剂经过８７３Ｋ空气预处理后，甲烷在９７３Ｋ的转化率约为１０％，催化剂的稳定性也得到较大程度的提高。ＴＰＳＲ实验结果表明，Ｒｕ的加入降低了芳烃生成的温度。ＴＰＯ和ＤＴＡ实验结果表明，在Ｍｏ－Ｒｕ／ＨＺＳＭ－５催化剂上可生成较多的碳物种，结合反应结果，可以认为反应过程中生成的碳物种对甲烷的无氧脱氢芳构化反应是起积极作用的     

[CuO-ZnO-Al2O3]/[HZSM-5]核壳双功能催化剂的制备、结构及其CO2+H2直接合成二甲醚反应性能

利用水热合成法制备了一系列不同晶化时间的核壳结构双功能催化剂[CuO-ZnO-Al₂O₃]/[HZSM-5],通过X射线衍射(XRD)、扫描电镜(SEM)和能量分散谱(EDS)对催化剂结构进行了表征,并考察了核壳催化剂CO₂加氢直接合成二甲醚的反应性能。结果表明,通过水热合成法可在甲醇合成催化剂CuO-ZnO-Al₂O₃表面包覆一层完整的HZSM-5分子筛膜,形成核壳结构,并且调节晶化时间可以控制分子筛晶粒尺寸及膜厚。与物理混合法制备的传统双功能催化剂相比,核壳结构催化剂合成二甲醚的选择性显著提高,其中晶化时间为3d的催化剂反应性能最为理想,CO₂转化率为38.9%,二甲醚选择性达到77.0%。     

Hydrogenation of p-Chloronitrobenzene on Nanosized Modified NiMoB Catalysts

NiMoB alloy catalyst has been reported to be a good catalyst for the hydrogenation of p-chloronitrobenzene to p-chloroaniline. The objective of this study was to investigate the effect of additives (Pd, La, Fe and Co) on the catalytic properties of NiMoB in the hydrogenation of p-chloronitrobenzene. The catalysts were prepared by chemical reduction method using sodium borohydride as the reducing agent. The molar ratios of Ni/Mo/B/additives in the starting materials were 0.4/1/3/0.1. The catalysts were characterized by inductively coupled plasma-mass spectrometry, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalysts were tested for liquid-phase hydrogenation of p-chloronitrobenzene at 1.2?MPa H₂ pressure and 333–353?K. Adding additives decreased the particle size of modified-NiMoB catalyst, suppressed the growth of the crystalline structure of NiMoB and helped the NiMoB nanocluster maintain its amorphous state. The reaction activity is in the order of the following: Pd-NiMoB?>?La-NiMoB?>?Co-NiMoB?>?NiMoB?>?Fe-NiMoB. Pd itself is the active metal for hydrogenation, but NiPd bimetallic alloy was too active resulting in low selectivity of chloroaniline. The other additives were in the form of hydroxide and acted as a spacer to prevent NiMoB catalysts from sintering and aggregation.     

Selective hydroisomerization of n-dodecane over platinum supported on zeolites

In this study, in order to develop catalysts for the selective isomerization of higher paraffin, the hydroisomerization reaction of n-dodecane was performed as a model reaction. Pt/ZSM-48, Pt/HZSM-5, Pt/HY, and Pt/SAPO-11 were examined for the selective hydroisomerization of n-dodecane. The catalysts were characterized via X-ray powder diffraction, N₂ adsorption, and the temperature-programmed desorption of ammonia. Among the catalysts studied, the Pt/HZSM-48 catalyst exhibited the best isomerization selectivity in the hydroisomerization reaction of n-dodecane, which is attributed to the moderate acid sites and medium-sized pores present in the HZSM-48. The highest iso-dodecane yield was obtained at a reaction temperature of 280 °C in the Pt/HZSM-48 catalyst. The optimal selectivity of the n-dodecane hydroisomerization over the Pt/SAPO-11 catalyst was obtained at approximately 300 °C, which was slightly higher than that of the Pt/HZSM-48 catalyst.     

助剂对泡沫金属微反应器内二甲醚水蒸气重整制氢的影响

采用共沉淀耦合机械混合法制备了CuO-ZnO-Al₂O₃/HZSM-5双功能催化剂用于二甲醚水蒸气重整制氢的研究,结合BET、H₂-TPR、XRD、SEM等表征手段,在泡沫金属微反应器内考察助剂Cr、Zr、Ce、Co对双功能催化剂催化性能的影响。研究结果表明,加入Cr助剂后, 可以有效降低催化剂的平均孔径和还原温度,并抑制催化剂制备过程中氢氧化锌晶相的形成,催化剂的低温催化性能明显提高,二甲醚的转化率和氢收率在较低温度下即可分别达到99%和95%,表现出了良好的低温反应活性。考察了反应温度、空速和水醚比等条件对二甲醚水蒸气重整催化剂催化活性的影响,在250℃、空速3 884 mL/(g·h)、水醚比为5的条件下,CuO-ZnO-Al₂O₃-Cr₂O₃/ HZSM-5催化二甲醚水蒸气重整反应进行50 h,二甲醚的转化率维持在97%以上,催化剂的活性没有明显下降。     

四丙基氢氧化铵改性纳米HZSM-5分子筛及其在甲醇制汽油中的催化性能

采用四丙基氢氧化铵(TPAOH)溶液对纳米ZSM-5分子筛进行改性, 运用X射线衍射、扫描电镜、²⁷Al和²⁹Si固体核磁、X射线光电子能谱、N₂物理吸附脱附法和NH₃程序升温脱附等手段对所制样品进行了表征, 并评价了其催化甲醇制汽油反应性能. 结果表明, 改性后的HZSM-5相对结晶度增加, 晶体形貌更加规整, 表面硅铝比增加, 比表面积和微孔表面积增大, 强酸位酸量增多. 同时, TPAOH改性不仅可以使分子筛脱硅脱铝, 而且伴有二次晶化补硅补铝, 改变了分子筛的硅铝分布. 改性的HZSM-5在甲醇制汽油反应中的稳定性大幅度提高, 其寿命由70h增至170h以上, 随着TPAOH处理时间的增加, 催化剂寿命增加, 氢转移反应加快, 导致油相产品中异构烷烃增多, 烯烃减少.     

NiFe双金属催化剂用于月桂酸甲酯加氢的研究

负载型Ni Fe/γ-Al₂O₃双金属催化剂的物理化学性质明显受还原温度的影响,进而影响月桂酸甲酯的加氢活性和产物选择性。金属Ni活性中心主要促进脱羰/脱羧(DOC)反应,Fe的加入能促进月桂酸甲酯发生加氢脱氧反应,促进C₁₂烷烃化合物生成。H₂-TPR、XRD、H₂-TPD和BET结果表明,高的还原温度有利于金属或合金活性中心形成,NiFe双金属催化剂的加氢活性取决于金属Ni、Fe和NiFe合金的含量;NiFe双金属催化剂吸附与活化H₂分子的能力明显受还原温度的影响。在研究的温度范围内,Ni活性中心具有优异的加氢和裂解性能,Fe物种的引入能有效抑制裂解性能。双金属催化剂的加氢活性顺序:NF420>NF360>NF450>NF300,在420℃下经H₂还原制得的NF420催化剂具有最佳的月桂酸甲酯加氢性能,在反应温度为380℃时,月桂酸甲酯加氢转化率和烷烃化合物选择性分别高达93.3%和90.0%。     

乙酰丙酸选择性加氢合成γ-戊内酯中高效和可循环使用的Ni3Fe NPs@C 双金属催化剂

生物质经催化转化合成燃料及化学品是当前研究的热点.目前,生物质的催化转化主要聚焦于纤维素、半纤维素和木质素的解聚及其下游产物合成.其中,乙酰丙酸(LA)作为纤维素解聚的主要产物之一,是一种极具竞争力的平台化合物和重要的生物质转化中间体.LA通过催化转化可以合成各类高附加值的化学品,例如,通过催化加氢LA可选择性合成γ-戊内酯(GVL).所合成的GVL用途广泛,可作为绿色溶剂、食品、燃料添加剂、(塑料、高分子、烃类或者其它高附加值化学品)前驱体等.目前,LA-to-GVL的研究主要着眼于非均相催化体系,包括负载型贵金属和非贵金属催化剂体.其中,贵金属催化剂主要有Ru,Au,Pd,Rh,Ir和Pt,虽然催化效率高,条件温和,但是成本高,难以实现工业化.此外对于广泛使用的Ru/C催化剂,存在金属-载体间相互作用不强.活性组分易流失、导致催化剂稳定性差等问题;而非贵金属则普遍存在催化活性不佳及反应条件苛刻等缺点.因此,开发高效、稳定、反应条件温和且具有工业化应用前景的非贵金属催化剂具有显著的研究意义,这也是当前的研究趋势.在特定温度下,金属离子与碳基底存在较强的相互作用.鉴于此,本文通过一步碳热还原法合成了活性炭负载的Ni3Fe双金属催化剂(Ni3Fe NPs@C).该催化剂在LA-to-GVL转化体系中展现了直接加氢(DH)和转移加氢(TH)双功能催化特性.首先,考察了其在DH体系中的反应特性:在130oC和2 MPa氢压反应条件下经2 h反应,LA转化率达到93.8％,GVL选择性为95.5％,GVL产率是相应的单金属Ni/C和Fe/C催化剂的6倍和40倍.此外,在TH催化反应体系中,在180oC,0.5 h和无外加氢源的反应条件下,以异丙醇为反应溶剂和供氢体,LA几乎完全转化为GVL,其反应效率同样相较于单金属Ni/C和Fe/C催化剂大幅度提高.所合成的Ni3Fe NPs@C双金属催化剂DH和TH催化性能优于绝大多数报道的LA加氢贵金属和非贵金属催化剂.而且,该催化剂具有良好的循环利用性能,经过四次循环,其结构和化学状态没有发生明显的改变,稳定性明显优于商业化的Ru/C催化剂.此外,通过系统分析其催化性能以及材料结构,明确了该催化剂在LA的DH和TH反应体系中的活性位点,并提出了可能的反应路径.该研究为其它类型的DH和TH反应体系以及生物质高效转化过程提供了新的催化剂设计思路.并且这种催化剂及其制备方法简单、绿色,易于工业化推广和应用.     

正丁烷在Au,Zn组合改性纳米HZSM-5上的催化转化

采用沉积沉淀和浸渍法制备了Au-Zn组合改性HZSM-5催化剂.并且对比研究了HZSM-5,Au/HZSM-5,Zn/HZSM-5和Au-Zn/HZSM-5催化剂的性质和催化性能.采用UV-Vis和XPS表征揭示出Au-Zn/HZSM-5催化剂中Au物种与Zn物种的相互作用.正丁烷探针反应结果表明,在Zn/HZSM-5催化剂中引入Au有效地提高了正丁烷的脱氢芳构化性能,同时抑制了正丁烷在Zn活性中心上的氢解副反应.在相同条件下,与Zn/HZSM-5催化剂相比,正丁烷转化率由49.1%增加到70.8%,烯烃和芳烃产物总选择性由57%增加到61.98%,干气的选择性由31%降低至28.4%.上述结果表明,Au-Zn/HZSM-5催化剂在轻烃芳构化反应中具有良好的催化性能.     

ACo_2O_4/HZSM-5催化剂上N_2O的直接分解

分别采用柠檬酸络合燃烧法和低温络合浸渍法制备尖晶石型复合金属氧化物催化剂ACo2O4(A=Mg,Ni,Zn)和分子筛负载尖晶石型复合金属氧化物催化剂ACo2O4/HZSM-5(A=Mg,Fe,Ni,Cu,Zn,Zr,La).采用X射线衍射(XRD)、氨程序升温脱附(NH3-TPD)、扫描电子显微镜(SEM)和X射线能谱(EDS)等手段对催化剂进行表征,并在固定床微型反应器中评价其催化分解N2O活性.实验结果表明,A位离子种类影响ACo2O4/HZSM-5催化剂活性,以Ni、Fe、Zr或La为A位离子时,催化剂的活性较好,N2O分解温度低.ACo2O4/HZSM-5催化剂的活性高于ACo2O4尖晶石型复合氧化物,一方面是ACo2O4在分子筛HZSM-5载体上高度分散,使其以超细颗粒形态存在,另一方面ACo2O4/HZSM-5催化剂具有适宜的酸性,可提高催化剂的活性.     

Xylene Synthesis Through Tandem CO2 Hydrogenation and Toluene Methylation Over a Composite ZnZrO Zeolite Catalyst

Selective synthesis of specific value-added aromatics from CO₂ hydrogenation is of paramount interest for mitigating energy and climate problems caused by CO₂ emission. Herein, we report a highly active composite catalyst of ZnZrO and HZSM-5 (ZZO/Z5-SG) for xylene synthesis from CO₂ hydrogenation via a coupling reaction in the presence of toluene, achieving a xylene selectivity of 86.5 % with CO₂ conversion of 10.5 %. A remarkably high space time yield of xylene could reach 215 mg g_cat⁻¹ h⁻¹, surpassing most reported catalysts for CO₂ hydrogenation. The enhanced performance of ZZO/Z5-SG could be due to high dispersion and abundant oxygen vacancies of the ZZO component for CO₂ adsorption, more feasible hydrogen activation and transfer due to the close interaction between the two components, and enhanced stability of the formate intermediate. The consumption of methoxy and methanol from the deep hydrogenation of formate by introduced toluene also propels an oriented conversion of CO₂.     

HZSM-5分子筛在甲醇制丙烯反应中的失活与再生

研究了甲醇制丙烯(MTP)催化剂经过多周期反应后失活的本质原因,据此提出了一种简便易行的催化剂再生方法,即二次晶化法,并将其应用到失活MTP催化剂的再生中。采用X射线衍射(XRD)、X射线荧光光谱(XRF)、X射线光电子能谱(XPS)、N₂吸附、²⁷Al魔角旋转固体核磁共振(²⁷Al MAS NMR)、NH₃程序升温脱附(NH₃-TPD)、吡啶吸附红外(Py-IR)光谱等测试技术对再生前后HZSM-5分子筛催化剂的晶体结构、硅铝比、织构性质、酸性质等进行了表征。并在常压(甲醇分压为30 kPa)、反应温度为470 ℃、甲醇质量空速(WHSV)为1 h^-1的条件下,研究了再生前后HZSM-5分子筛催化剂的催化性能。结果表明,分子筛晶体结构被破坏、活性位流失是多周期反应后HZSM-5分子筛催化剂活性下降的主要原因。经过二次晶化再生后,催化剂的相对结晶度、比表面积、孔容和酸量都明显提高,晶体结构和活性位得到了有效修复,再生催化剂在MTP反应中重新表现出优异的甲醇转化能力和丙烯选择性。     

不同锌盐改性的HZSM-5催化剂上甲醇芳构化反应

分别用ZnSO4,Zn(AcO)2,Zn(NO3)2和ZnCl2溶液对HZSM-5分子筛浸渍改性得到不同Zn盐改性的HZSM-5催化剂.采用X射线衍射、N2物理吸附、热重-质谱分析、氨程序升温脱附和吡啶吸附红外光谱等方法对改性后的催化剂进行了表征,并在固定床反应装置上考察了其甲醇芳构化反应性能.结果表明,不同Zn盐改性的HZSM-5催化剂上Zn物种的存在形式不同会导致其表面酸中心强度与分布具有较大差异,经ZnSO4改性的HZSM-5催化剂表面上强B酸中心和Zn物种的存在使其表现出最佳的甲醇芳构化反应性能.