Direct production of hydrogen peroxide over bimetallic CoPd catalysts:Investigation of the effect of Co addition and calcination temperature

A series of CoPd/KIT-6 bimetallic catalysts with various Co:Pd molar ratios at different calcination temperatures were prepared and used for the direct synthesis of H_(2)O_(2) from H_(2) and O_(2).These catalysts were characterized by nitrogen adsorption-desorption,low and wide-angle X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),scanning electron microscopy(SEM),elemental mapping and energy-dispersive X-ray(EDX)methods.It was found that the particle size,electronic interactions,morphology,and textural properties of these catalysts as well as their catalytic activity in the reaction of H_(2) with O_(2) were affected by Co addition and different calcination temperatures.Also,the results showed that while the H_(2)O_(2) selectivity depends on Pd^(2+) species,the H_(2) conversion is related to Pd0 active sites.Among these catalysts,CoPd/KIT-6 calcined at 350℃(CoPd/KIT-350 catalyst)showed the best catalytic activity with 50%of H_(2)O_(2) selectivity and 51%conversion of H_(2).

EFFECT OF ELECTRON DONORS ON THE SELECTIVE HYDROGENATION OF DIENE TO MONOENE OVER HETEROGENIZED Pd CATALYST

In the selective hydrogenation of diene (or alkyne) using heterogenized homogeneous catalyst, the high selectivity of monoene formation only appears in a very short time interval. The addition of suitable electron donors can decrease or even cease the monoene hydrogenation and thereby keep the high monoene selectivity after reaching its maximum.

Effect of cobalt oxide on performance of Pd catalysts for lean-burn natural gas vehicles in the presence and absence of water vapor

Pd-based catalysts modified by cobalt were prepared by co-impregnation and sequential impregnation methods,and characterized by X-ray powder diffraction （XRD）,N2 adsorption/desorption （Brunauer-Emmet-Teller method）,CO-chemisorption and X-ray photoelectron spectroscopy （XPS）.The activity of Pd catalysts was tested in the simulated exhaust gas from lean-burn natural gas vehicles.The effect of Co on the performance of water poisoning resistance for Pd catalysts was estimated in the simulated exhaust gas with and without the presence of water vapor.It was found that the effect of Co significantly depended on the preparation process.PdCo/La-Al2O3 catalyst prepared by co-impregnation exhibited better water-resistant performance.The results of XPS indicated that both CoAl2O4 and Co3O4 were present in the Pd catalysts modified by Co.For the catalyst prepared by sequential impregnation method,the ratio of CoAl2O4/Co3O4 was higher than that of the catalyst prepared by co-impregnation method.It could be concluded that Co3O4 played an important role in improving water-resistant performance.

Catalytic Performance and Characterization of Anatase TiO_(2) Supported Pd Catalysts for the Selective Hydrogenation of Acetylene

Anatase TiO_(2)nanospindles containing 89%exposed{101}facets(TIO_(2)-101)and nanosheets with 77%exposed{001}facets(TiO_(2)-001)were hydrothermally synthesized and used as supports for Pd catalysts.The effects of the TiO_(2)materials on the catalytic performance of Pd/TiO_(2)-101 and Pd/TiO_(2)-001 catalysts were investigated in the selective hydrogenation of acetylene to polymer-grade ethylene.The PdfTiO_(2)-101 catalyst exhibited enhanced performance in terms of acetylene conversion and ethylene yield.To understand these effects,the catalysts were characterized by H_(2)temperature-programmed desorption(H_(2)-TPD),H_(2)temperature-programmed reduction(H=-TPR),transmission electron microscopy(TEM),pulse CO chemisorption,X-ray photoelectron spectroscopy(XPS),and thermogravimetric analysis(TGA).The TEM and CO chemisorption results confirmed that Pd nanoparticles(NPs)on the TiO_(2)-101 support had a smaller average particle size(1.53 nm)and a higher dispersion(15.95%)than those on the TiO_(2)-001 support(average particle size of 4.36 nm and dispersion of 9.06%).The smaller particle size and higher dispersion of Pd on the Pd/TiO_(2)-101 catalyst provided more reaction active sites,which contributed to the improved catalytic activity of this supported catalyst.

Lean methane combustion over zeolite-supported Pd catalysts:Structure-performance relationship and deactivation mechanism

Zeolites are a promising support for Pd catalysts in leanmethane(CH_(4))combustion.Herein,three types of zeolites(H-MOR,H-ZSM-5 and H-Y)were selected to estimate their structural effects and deactivation mechanisms in CH_(4)combustion.We show that variations in zeolite structure and surface acidity led to distinct changes in Pd states.Pd/H-MOR with external high-dispersing Pd nanoparticles exhibited the best apparent activity,with activation energy(Ea)at 73 kJ/mol,while Pd/H-ZSM-5 displayed the highest turnover frequency(TOF)at 19.6×10^(−3)sec^(−1),presumably owing to its large particles with more step sites providing active sites in one particle for CH_(4)activation.Pd/H-Y with dispersed PdO within pore channels and/or Pd2+ions on ion-exchange sites yielded the lowest apparent activity and TOF.Furthermore,Pd/H-MOR and Pd/H-ZSM-5 were both stable under a dry condition,but introducing 3 vol.%H_(2)O caused the CH_(4)conversion rate on Pd/H-MOR drop from 100%to 63%and that on Pd/H-ZSM-5 decreased remarkably from 82%to 36%.The former was shown to originate fromzeolite structural dealumination,and the latter principally owed to Pd aggregation and the loss of active PdO.

Pd催化剂表面物种对丙炔加氢性能的影响

采用H_(2)-TPR-MS-IR、CO脉冲吸附、He-TPD、H_(2)-TPR-MS、AFM-IR等方法研究了Pd催化剂的表面物种及Pd金属分散度,确定了Pd催化剂的表面物种状态,分析了Pd催化剂的表面物种与催化剂丙炔加氢性能的关系。实验结果表明,Pd催化剂表面存在碳物种和氮物种,碳物种和氮物种在800℃以上可被完全脱除。Pd催化剂表面存在的碳物种和氮物种更有利于Pd的分散,促使反应向预期的方向进行,阻碍丙烯的进一步加氢,从而有利于选择性丙炔加氢反应。

Enhanced stability of nitrogen-doped carbon-supported palladium catalyst for oxidative carbonylation of phenol

Enhancing the stability of supported noble metal catalysts emerges is a major challenge in both science and industry.Herein,a heterogeneous Pd catalyst(Pd/NCF)was prepared by supporting Pd ultrafine metal nanoparticles(NPs)on nitrogen-doped carbon;synthesized by using F127 as a stabilizer,as well as chitosan as a carbon and nitrogen source.The Pd/NCF catalyst was efficient and recyclable for oxidative carbonylation of phenol to diphenyl carbonate,exhibiting higher stability than Pd/NC prepared without F127 addition.The hydrogen bond between chitosan(CTS)and F127 was enhanced by F127,which anchored the N in the free amino group,increasing the N content of the carbon material and ensuring that the support could provide sufficient N sites for the deposition of Pd NPs.This process helped to improve metal dispersion.The increased metal-support interaction,which limits the leaching and coarsening of Pd NPs,improves the stability of the Pd/NCF catalyst.Furthermore,density functional theory calculations indicated that pyridine N stabilized the Pd^(2+)species,significantly inhibiting the loss of Pd^(2+)in Pd/NCF during the reaction process.This work provides a promising avenue towards enhancing the stability of nitrogen-doped carbon-supported metal catalysts.

Pt-Pd-Ni体系相图与热力学研究进展

铂基催化剂具有活性高、选择性好、电化学稳定性佳等优点,在工业催化和燃料电池领域具有非常重要的地位。然而,由于成本较高、可用性较低限制了其实际发展。因此,有必要优化铂基催化剂的利用率,设计低成本和高稳定性的铂基催化剂。本研究首先介绍了在燃料电池催化剂领域具有应用前景的Pt-Pd-Ni系合金电催化剂的发展和研究现状,然后详细介绍了Pt-Pd-Ni体系的三个二元系相图与热力学评估数据和研究进展,并对Pt-Pd-Ni三元系的一些实验研究进展和今后的研究工作提出展望,对不同相结构对催化性能的影响进行了分析和讨论。通过Pt-Pd-Ni系相图和相结构等的研究将为燃料电池用新型贵金属合金催化材料的设计及工业应用奠定理论和实验基础。

负载型Pd催化剂催化草酸二甲酯脱羰基制备碳酸二甲酯

为开发高效、成本低廉的碳酸二甲酯(DMC)合成工艺,以Naβ(25)、NaZSM-5(25)、NaY(6)、NaY(8)和NaY(10)分子筛为载体,采用浸渍法制备了负载型Pd催化剂,并将其首次用于草酸二甲酯(DMO)脱羰基反应。采用X射线衍射、X射线光电子能谱、透射电镜和傅里叶变换红外光谱等表征方法对催化剂的组成、价态、孔结构、形貌以及晶型进行分析,并对其催化性能进行评价。结果表明,使用Pd/NaY(6)催化剂催化DMO脱羰基合成DMC,在反应温度220℃、反应时间90 min、催化剂用量1.0 g、1,4-二氧六环与DMO质量比4∶1、Pd负载量(w)0.2%的条件下,DMO转化率可达82.59%,DMC选择性可达62.33%。通过对催化剂稳定性的研究发现,经过5次循环再生后,催化剂对DMO脱羰基反应仍具有良好的催化活性。最后,合理推测出Pd/NaY(6)催化剂催化DMO脱羰基合成DMC的反应机理。

1,4-丁炔二醇选择性加氢催化剂:Pd/ZrO_(2)及其碱金属改性

以Zr(OH)_(4)焙烧得到的ZrO_(2)为载体,采用等体积浸渍法制备了负载型Pd/ZrO_(2)和碱金属(M)改性的催化剂(Pd/M/ZrO_(2)),通过XRD、BET、TEM及HRTEM、CO_(2)-TPD、XPS对催化剂进行了表征,并评价了其在1,4-丁炔二醇(BYD)选择性加氢制1,4-丁烯二醇(BED)反应中的活性、选择性和稳定性,探究了反应气氛及碱金属改性对其活性和稳定性的影响。结果表明,1.0%Pd/ZrO_(2)(1.0%为Pd的质量分数)在50℃,2.40 MPa H_(2)下,能够催化BYD选择性加氢生成BED,有较高的催化活性[0.048 molBYD/(g Pd·s)],在BYD完全转化的条件下,BED的选择性为91.2%。氨的引入能够显著抑制催化剂加氢活性,提高BED的选择性。在BYD接近完全转化时,BED的选择性可达95.6%。向ZrO_(2)载体中引入少量碱金属(Li、Na、K、Rb、Cs),能够提高BED的选择性,其中,Rb的影响最为显著,BED的选择性可达94.1%。

N掺杂活性炭负载Pd催化对甲酰基苯甲酸选择性加氢

采用等体积浸渍法制备了N掺杂活性炭负载的Pd(Pd/WH-C)催化剂,通过N_(2)吸附-脱附、FTIR、SEM、TEM、XRD、XPS、H_(2)-TPR等手段对催化剂进行了表征,并将Pd/WH-C催化剂用于对甲酰基苯甲酸(4-CBA)选择性加氢反应,比较了它与商业Pd/C催化剂的催化性能。表征结果显示,N掺杂提高了活性炭载体的比表面积、介孔体积及Pd纳米颗粒的分散度,增强了Pd纳米颗粒与活性炭之间的相互作用,有效抑制了Pd纳米颗粒的流失和烧结。实验结果表明,在280℃和7.7 MPa条件下反应1 h,Pd/WH-C催化剂上4-CBA的初始转化率为97.5%,催化剂循环使用6次后4-CBA转化率下降38.4百分点,优于商业Pd/C催化剂,显示出良好的稳定性。

基于密度泛函理论的2-乙基蒽醌在Pd催化剂上的加氢机理

采用密度泛函理论方法研究了2-乙基蒽醌(eAQ)和H_(2)分子在Pd(111)催化剂上的吸附行为。结果表明,eAQ平行吸附在Pd(111)表面,金属Pd转移了部分电子给eAQ;H_(2)分子在Pd(111)面上发生了解离吸附,且解离能垒较低,表明金属Pd具有较强的H_(2)催化解离能力。在此基础上,根据eAQ的Fukui(0)指数和前线轨道等电子结构性质分析,研究了eAQ加氢机理,提出了eAQ加氢生成2-乙基蒽氢醌(eAQH_(2))的2条可能的反应路径,路径1是H自由基先进攻离乙基近的羰基O原子,路径2是H自由基先进攻离乙基远的羰基O原子。研究发现,Pd催化剂催化蒽醌加氢选择性较高的原因,一是与eAQ自身电子结构性质相关,二是生成副产物的反应能垒远高于主反应。

Pd/C催化剂在间硝基苯磺酸钠加氢反应中的应用

间氨基苯磺酸钠是一种重要的化工中间体,可由多种方法制备得到,催化加氢法是目前主要使用的方法,但工业化报道较少,这是由于在间硝基苯磺酸钠加氢合成间氨基苯磺酸钠的液相反应中催化剂存在失活现象,难以多次套用,工业化成本高。使用自制Pd/C催化剂进行间硝基苯磺酸钠的液相加氢反应,采用液相色谱-四级杆飞行时间串联质谱(LC-QTOF-MS)、X射线衍射谱(XRD)、X射线光电子能谱(XPS)、BET表面分析等方法对Pd/C催化剂的失活原因进行探究,确定催化剂的失活原因。Pd/C催化剂的失活是由于在硝基选择性加氢过程中,原料间硝基苯磺酸钠转化为偶氮化合物或氧化偶氮化合物,由于这些中间体的吸附性较强,易堵塞活性炭载体的孔道,造成催化剂比表面积减少,导致催化剂暂时性的中毒失活,而并非是加氢还原了原料中磺酸基团生成硫化钯而导致的催化剂永久性失活。

Pd/NC催化剂高效催化糠醛选择性加氢制糠醇的研究

利用高温热解金属有机框架(MOFs)制备不同Pd负载量(0.1%、1%、5%)的氮掺杂碳负载Pd纳米颗粒催化剂(Pd/NC),考察了其催化糠醛选择性加氢性能。当Pd负载量为0.1%时,Pd/NC催化剂在反应温度为120℃、反应压力为3.0 MPa H_(2)的条件下催化糠醛加氢反应4 h,糠醛转化率为93.8%,糠醇选择性为86.7%,糠醇收率为81.4%。利用SEM、TEM、HRTEM、XRD、XPS、STEM和STEM-EDX元素面扫等表征手段对催化剂的结构和形貌进行表征与分析,结果表明,高分散的小尺寸Pd金属纳米粒子与载体之间存在着协同作用,使催化剂表现出优异的催化糠醛选择性加氢制糠醇性能。

Pd基催化剂载体对天然气催化燃烧影响的研究进展

天然气广泛应用于化学品合成和交通运输等领域。甲烷作为天然气的主要成分,具有强温室效应,其不完全燃烧会对环境产生不利影响。催化燃烧技术是解决甲烷不完全燃烧问题的有效方法,其中钯(Pd)基催化剂是该技术的核心,而载体是影响Pd基催化剂甲烷催化燃烧催化活性的重要因素。首先,阐述了甲烷催化燃烧的机理。其次,总结了近年来国内外Pd基催化剂的研究进展:对于多孔颗粒载体型Pd基催化剂,研究聚焦于提升Pd分散性、稳定性与耐热性,以增强催化活性并降低Pd负载量,从而减少成本;而对于整体型Pd基催化剂,研究聚焦于提升有效比表面积、传热传质效率与结构稳定性,以适应大通量甲烷催化燃烧。最后,对用于甲烷催化燃烧的Pd基催化剂载体的未来研究发展趋势进行了展望,包括优化整体型Pd基催化剂骨架载体的涂敷工艺以提高催化效率、采用新型材料替代传统载体材料以制备高性能催化剂,以及进行载体全周期寿命实验以确保催化剂的长期稳定性。

Pd/SBA-15-NH_(2)制备及其催化甲酸分解制氢

制备了介孔分子筛SBA-15,对其进行氨基功能化得到SBA-15-NH_(2)载体,采用液相还原法制备了负载超细Pd纳米催化剂,利用X射线衍射仪(XRD)和透射电镜(TEM)对催化剂的结构和形貌进行了分析,并将制备的催化剂用于甲酸脱氢反应。结果表明,氨基的引入使得Pd纳米颗粒在载体上均匀分布,平均粒径仅为2.43 nm。在反应温度为313 K、甲酸/甲酸钠物质的量比为5∶3、甲酸浓度为5 mol·L^(-1)的条件下,甲酸脱氢反应的表观TOF值可达5610 h^(-1),氢气选择性接近100%。

Pd-ZnIn_(2)S_(4)负载型催化剂光催化降解水中阿特拉津

光催化降解水体中痕量除草剂阿特拉津(ATZ)可有效消除其对水生态环境及人体健康的潜在危害。以鹅卵石为载体,采用简便的胶粘法制备Pd-ZnIn_(2)S_(4)负载型催化剂,氙灯光源下开展光催化降解水中ATZ试验,同时对催化剂形貌特征和光学特性进行了表征。结果发现,鹅卵石负载型催化剂禁带宽度变小、比表面积增大,光催化降解水中ATZ活性良好;鹅卵石负载型催化剂选用环氧树脂为最佳粘结剂,0.1wt%Pd-ZnIn_(2)S_(4)粉末最佳黏附量为100 mg;薄涂方式制备的鹅卵石负载型催化剂对初始浓度5 mg/LATZ的光降解效率为62%,大于厚涂的41%。这是因为环氧树脂薄涂既能固定催化剂,又不会使催化剂被环氧树脂完全包裹而影响活性组分活性。

Pd基MoO_(x)催化剂中金属与载体的相互作用及其对Heck反应的影响

钯(Pd)催化的Heck反应是合成中构建碳-碳键的有效方法之一。金属-载体相互作用(MSI)对于非均相催化剂在某些工业过程中由于金属活性位点暴露或堵塞而显著提高或降低催化性能具有重要意义。本文合成了Pd基MoO_(x)催化剂,利用XRD、XPS、Raman等表征研究了在不同氧化还原处理条件下,钯纳米粒子与氧化钼层的金属-载体相互作用(MSI)在碘苯和丙烯酸甲酯的Heck反应中的性能影响。研究发现Pd/MoO_(3)在氢气条件下的部分还原导致MoO_(x)物种迁移到Pd-NPs的表面并形成包封结构,涂层可能通过空气煅烧重新暴露,MSI导致Pd/MoO_(3)在Heck反应中的催化性能降低。本研究证明了平衡金属-载体相互作用在实际催化剂设计中的重要性,以实现贵金属催化剂在催化Heck反应中的更高利用率。

Pd/SiC催化苯乙酮加氢反应的性能

以高比表面积SiC为载体,采用液相还原法制备了Pd/SiC催化剂,通过XRD,TEM,XPS等方法对催化剂进行了表征,研究了Pd/SiC催化剂催化苯乙酮加氢反应的性能,探讨了催化过程中SiC表面对苯乙酮的活化作用。实验结果表明,3%(w)Pd/SiC催化剂可在室温和常压H_(2)条件下高效催化苯乙酮加氢反应,反应4 h后苯乙酮转化率和1-苯乙醇选择性均能达到95%以上。TEM和XRD表征结果显示,Pd颗粒在SiC表面分散均匀,颗粒平均尺寸约3.1 nm。催化剂稀释实验结果表明,SiC载体表面可以吸附并活化苯乙酮,催化过程中苯乙酮在SiC表面活化,H_(2)在Pd表面解离产生活性氢,活性氢溢流到SiC表面与苯乙酮发生加氢反应。

醋酸乙酯在Pd/Au表面的形成机理研究

采用密度泛函理论研究了醋酸乙烯合成过程中关键副产物醋酸乙酯在Pd/Au(100)及Pd/Au(111)表面的形成机理,从微观层面揭示Pd/Au(100)及Pd/Au(111)表面不同Pd原子数、Pd/Au原子构型对醋酸乙酯形成的影响。研究结果表明,Pd/Au(100)和Pd/Au(111)表面邻位Pd活性位构型最有利于醋酸乙酯的生成,而随着Pd/Au表面Pd原子数的增加,生成醋酸乙酯的反应活性逐渐降低,团簇Pd活性位(Pd原子数大于等于4)可以有效抑制醋酸乙酯的生成。该机理为开发高选择性Pd/Au催化剂、抑制醋酸乙酯副产物生成提供了理论依据。