表面等离激元增强Ni/TiO2光催化苯乙炔选择性加氢

研究采用浸渍还原法制备了碳修饰的二氧化钛负载的Ni纳米颗粒催化剂，在苯乙炔选择性加氢反应中表现出良好的光催化性能。Ni纳米颗粒在可见光激发下产生高能“热电子”促进了反应底物的解离和活化。富电子态的Ni纳米颗粒抑制了苯乙烯在Ni/TiO₂表面的吸附，提高了苯乙烯的选择性。本工作为光催化苯乙炔选择性加氢反应提供了一种绿色且高效的方法。     

负载型Pd/TiO2和Pd-Ag/TiO2催化剂的乙炔选择性加氢催化性能

利用程序升温还原(TPR)、X-射线衍射(XRD)、CO吸附-红外光谱(CO-IR)、电子顺磁共振(EPR)和微型催化反应评价等手段, 研究了负载Pd/γ-Al2O3, Pd/TiO2和Pd-Ag/TiO2催化剂的结构和乙炔选择性加氢催化性能. 结果表明, Pd/TiO2催化剂具有较Pd/γ-Al2O3催化剂更优良的乙炔选择性加氢催化性能, 这与Pd-TiO2之间的强相互作用密切相关. Pd-TiO2之间的强相互作用不仅使负载型钯金属催化剂具有较高的乙炔加氢催化选择性, 而且具有较高的乙炔加氢催化活性. Pd/TiO2催化剂中添加Ag 组分后, Pd金属可促进Ag+的还原并可能形成Pd-Ag合金, 催化剂的乙烯选择性虽有所增加, 但乙炔转化率和乙烯收率下降.     

Pt在MgAl2O4载体上的分散程度对催化苯甲醛加氢反应影响

构建催化剂特别是在亚纳米尺度下分散的贵金属催化剂的构效关系是多相催化研究领域中的主要任务之一.我们采用与金属Pt具有强相互作用的MgAl2O4尖晶石作为载体,通过简单浸渍法制备了在纳米、亚纳米和单原子尺度上分散的Pt催化剂.首先利用X射线衍射和原子分辨的球差校正电镜,确定了Pt在MgAl2O4尖晶石载体表面上随负载量增大逐渐形成孤立的和相邻的单原子Pt,然后逐渐形成无定形Pt聚集体和小晶粒;然后利用电感耦合等离子体光谱和CO化学吸附测定了催化剂中Pt的含量和分散度;进一步通过测定CO在Pt表面吸附的红外光谱,区分了载体表面单原子和金属颗粒表面原子的CO吸附特征结构,并据此对不同结构的Pt原子进行了半定量估算.考察了具有不同Pt分散结构的Pt/MgAl2O4催化剂的催化苯甲醛选择性加氢能力,发现以载体表面Pt单原子物种为主的催化剂,可在较宽的温度区间内保持较高的部分加氢产物苯甲醇的选择性(60–150oC,苯甲醇选择性99.4–97.9％,甲苯选择性～0.4％),而以Pt纳米颗粒为主的催化剂上苯甲醇选择性降低显著,同时生成较多深度加氢产物甲苯(60–150oC,苯甲醇选择性99.0–93.1％,甲苯选择性0.7–5.0％).此外,我们测定了各催化剂在不同转化率(～20–90％)时催化剂加氢反应的质量比活性和转化频率(TOF),并在较低苯甲醛转化率(～20％)时,估算了不同结构Pt物种对苯甲醛加氢反应的本征活性,发现Pt纳米颗粒表面原子比MgAl2O4载体表面Pt单原子本征活性更高(4807 h–1 versus 3277 h–1).综上,Pt单原子催化剂具有贵金属原子利用率高,本征活性和加氢选择性高等优点;Pt纳米催化剂表面原子深度加氢能力强,加氢选择性较差,虽本征活性更高,但不足以补偿贵金属原子利用率降低带来的活性损失,Pt质量比活性显著低于单原子催化剂.此外,MgAl2O4尖晶石负载的单原子Pt催化剂也具有良好的催化反应循环稳定性,是一种较为理想的催化苯甲醛选择性加氢制苯甲醇催化剂.     

Pt在MgAl_2O_4载体上的分散程度对催化苯甲醛加氢反应影响（英文）

构建催化剂特别是在亚纳米尺度下分散的贵金属催化剂的构效关系是多相催化研究领域中的主要任务之一.我们采用与金属Pt具有强相互作用的Mg Al_2O_4尖晶石作为载体,通过简单浸渍法制备了在纳米、亚纳米和单原子尺度上分散的Pt催化剂.首先利用X射线衍射和原子分辨的球差校正电镜,确定了Pt在Mg Al_2O_4尖晶石载体表面上随负载量增大逐渐形成孤立的和相邻的单原子Pt,然后逐渐形成无定形Pt聚集体和小晶粒;然后利用电感耦合等离子体光谱和CO化学吸附测定了催化剂中Pt的含量和分散度;进一步通过测定CO在Pt表面吸附的红外光谱,区分了载体表面单原子和金属颗粒表面原子的CO吸附特征结构,并据此对不同结构的Pt原子进行了半定量估算.考察了具有不同Pt分散结构的Pt/Mg Al_2O_4催化剂的催化苯甲醛选择性加氢能力,发现以载体表面Pt单原子物种为主的催化剂,可在较宽的温度区间内保持较高的部分加氢产物苯甲醇的选择性(60–150oC,苯甲醇选择性99.4–97.9%,甲苯选择性~0.4%),而以Pt纳米颗粒为主的催化剂上苯甲醇选择性降低显著,同时生成较多深度加氢产物甲苯(60-150oC,苯甲醇选择性99.0–93.1%,甲苯选择性0.7–5.0%).此外,我们测定了各催化剂在不同转化率(~20–90%)时催化剂加氢反应的质量比活性和转化频率(TOF),并在较低苯甲醛转化率(~20%)时,估算了不同结构Pt物种对苯甲醛加氢反应的本征活性,发现Pt纳米颗粒表面原子比Mg Al_2O_4载体表面Pt单原子本征活性更高(4807 h–1 versus 3277 h–1).综上,Pt单原子催化剂具有贵金属原子利用率高,本征活性和加氢选择性高等优点;Pt纳米催化剂表面原子深度加氢能力强,加氢选择性较差,虽本征活性更高,但不足以补偿贵金属原子利用率降低带来的活性损失,Pt质量比活性显著低于单原子催化剂.此外,Mg Al_2O_4尖晶石负载的单原子Pt催化剂也具有良好的催化反应循环稳定性,是一种较为理想的催化苯甲醛选择性加氢制苯甲醇催化剂.     

调控炔烃半氢化反应的催化选择性:实验和理论的最新进展（英文）

由于短链烯烃的广泛应用,炔烃选择性加氢制备烯烃是一个非常重要的石油化学催化过程.其中最简单的乙炔半氢化,吸引了众多研究者的广泛研究,是催化选择性调控的一个非常重要反应.工业上,由石油蒸汽裂解得到的乙烯往往混有微量(¹%)的乙炔,它会毒化乙烯聚合反应时所使用的Ziegler-Natta催化剂,因此需要降低乙炔含量至5×10–6以下.这要求加氢催化剂具有很高的乙炔转化率(> 99%)和乙烯选择性(> 80%).Pd基催化剂因低温下的具有高活性,是最常用的炔烃半氢化催化剂,其中Pd-Ag合金催化剂已在工业界应用了数十年.近十几年来,新型的乙炔半氢化催化剂不断被提出,其催化选择性的研究也取得了很大的进展.本文对炔烃半氢化反应的最新研究进展进行了总结.以乙炔加氢为例,介绍了其工业反应的条件、反应的网络以及潜在的副反应.归纳了提高加氢选择性的常见方法,并总结了近十几年报道的性能较好的乙炔半氢化催化剂.重点阐述了近年研究对加氢选择性的深入理解:Pd基催化剂的表面结构会随着反应条件和反应过程动态变化,从而影响加氢选择性.利用程序升温脱附和X射线光电子能谱研究催化剂的表...     

Pt/TiO_2催化剂的制备及其在氨催化氧化中的应用

二氧化钛具有优良的光催化性能,以其为载体通过光催化还原沉积可在其表面实现单质金属活性组分负载.选择二氧化钛颗粒为载体,通过紫外光照射在二氧化钛颗粒表面还原沉积铂单质,形成Pt/TiO2负载型催化剂,并将该新型催化剂用于氨催化氧化反应.所制备的Pt/TiO2催化剂铂负载量减为0.2 gPt/gTiO2,比表面积增达10 m2/g.以该催化剂催化氨氧化反应,氨转化率在600~700℃即可达100%,低于目前硝酸工业中氨氧化反应温度800~900℃,也低于PtO2升华温度850℃.该催化剂经400 h连续反应,其铂载量、及催化活性均无降低,具有工业应用前景.     

光照和加热条件下Pt/TiO_2催化二氧化碳加氢(英文)

浸渍法制备了Pt负载量为0.5 to 2%的Pt/TiO2催化剂,考察它们在光照和加热条件下二氧化碳催化加氢性能.结果表明,二氧化碳加氢反应均可在Pt/TiO2的催化下进行,但在不同反应条件下加氢反应通过不同方式进行.在加热条件下,二氧化碳可转化为一氧化碳和甲烷,且在低温加热条件下一氧化碳是主产物(CO选择性为100%,250℃,0.5%Pt/TiO2).在1.5%Pt/TiO2催化剂上,当反应温度从250℃升高到450℃时,CH4的选择性由0增加到60.94%.同时,增加Pt的负载量也会导致CH4的选择性的增加.然而,在光照条件下,产物只有甲烷.CO2-TPD结果表明,二氧化碳通过羰基基团与作为吸附中心的Pt相连接.结合催化活性与表征结果,提出在光照条件下,反应可能以二氧化碳和氢气分别被光生电子活化反应生成甲酸中间体,随后经由甲酸加氢和脱水生成甲烷的机理进行.而在加热条件下,反应可能以二氧化碳首先吸附在催化剂表面形成羰基Pt物种,随后加氢生成一氧化碳,一氧化碳继续加氢生成甲烷的机理进行.     

The photocatalytic and thermal catalytic reduction of CO2 with H2 over Pt/TiO2 catalysts

浸渍法制备了Pt负载量为0.5 to 2%的Pt/TiO2催化剂,考察它们在光照和加热条件下二氧化碳催化加氢性能.结果表明,二氧化碳加氢反应均可在Pt/TiO2的催化下进行,但在不同反应条件下加氢反应通过不同方式进行.在加热条件下,二氧化碳可转化为一氧化碳和甲烷,且在低温加热条件下一氧化碳是主产物(CO选择性为100%,250℃,0.5%Pt/TiO2).在1.5%Pt/TiO2催化剂上,当反应温度从250℃升高到450℃时,CH4的选择性由0增加到60.94%.同时,增加Pt的负载量也会导致CH4的选择性的增加.然而,在光照条件下,产物只有甲烷.CO2-TPD结果表明,二氧化碳通过羰基基团与作为吸附中心的Pt相连接.结合催化活性与表征结果,提出在光照条件下,反应可能以二氧化碳和氢气分别被光生电子活化反应生成甲酸中间体,随后经由甲酸加氢和脱水生成甲烷的机理进行.而在加热条件下,反应可能以二氧化碳首先吸附在催化剂表面形成羰基Pt物种,随后加氢生成一氧化碳,一氧化碳继续加氢生成甲烷的机理进行.     

SiO2负载壳聚糖希夫碱钯催化剂对苯丙酮催化加氢的研究

以SiO2负载的壳聚糖水杨醛希夫碱钯配合物为催化剂,在40℃的较低温度和常压氢气的温和条件下,将苯丙酮催化加氢为丙苯,实现了芳香羰基向亚甲基的还原转化.系统考察了溶剂、反应时间、反应温度和催化剂用量等因素对苯丙酮催化加氢反应的影响.结果表明,SiO2负载壳聚糖希夫碱钯催化剂具有优良的催化苯丙酮加氢为丙苯的活性和选择性.     

Pt/TiO2催化剂的制备及其在氨催化氧化中的应用

二氧化钛具有优良的光催化性能,以其为载体通过光催化还原沉积可在其表面实现单质金属活性组分负载。本研究选择二氧化钛颗粒为载体,通过紫外光照射在二氧化钛颗粒表面还原沉积铂单质,形成Pt/ TiO2核壳结构,并将该新型催化剂用于氨催化氧化反应。所制备的Pt/TiO2催化剂铂负载量减为0.2 gPt/ gTiO2,比表面积增达10 m2/ g。以该催化剂催化氨氧化反应,氨转化率在600-700 篊即可达100 %,低于目前硝酸工业中氨氧化反应温度800-900 篊,也低于PtO2升华温度850 篊。该催化剂经400 h连续反应,其铂载量、及催化活性均无降低,具有工业应用前景。     

Encapsulation of Palladium Carbide Subnanometric Species in Zeolite Boosts Highly Selective Semihydrogenation of Alkynes

The selective hydrogenation of alkynes to alkenes is a crucial step in the synthesis of fine chemicals. However, the widely utilized palladium (Pd)-based catalysts often suffer from poor selectivity. In this work, we demonstrate a carbonization-reduction method to create palladium carbide subnanometric species within pure silicate MFI zeolite. The carbon species can modify the electronic and steric characteristics of Pd species by forming the predominant Pd−C₄ structure and, meanwhile, facilitate the desorption of alkenes by forming the Si−O−C structure with zeolite framework, as validated by the state-of-the-art characterizations and theoretical calculations. The developed catalyst shows superior performance in the selective hydrogenation of alkynes over mild conditions (298 K, 2 bar H₂), with 99 % selectivity to styrene at a complete conversion of phenylacetylene. In contrast, the zeolite-encapsulated carbon-free Pd catalyst and the commercial Lindlar catalyst show only 15 % and 14 % selectivity to styrene, respectively, under identical reaction conditions. The zeolite-confined Pd-carbide subnanoclusters promise their superior properties in semihydrogenation of alkynes.     

Exfoliated and reorganized graphite oxide on titania nanoparticles as an auxiliary co-catalyst for photocatalytic solar conversion

The hybrid of graphite oxide (GO)/TiO(2) was prepared through the spontaneous exfoliation of bulky graphite oxide and reorganization with TiO(2) nanoparticles as a solar conversion and hydrogen-generating photocatalyst. GO/TiO(2) showed enhanced activities for both photocurrent generation (in an electrode form) and hydrogen production (in a slurry form) than those of bare TiO(2) under UV light irradiation. The enhanced photocatalytic activity of GO/TiO(2) is ascribed to the ability of graphitic layers in accepting and transporting electrons from excited TiO(2), promoting the charge separation. When GO was hybridized with platinized TiO(2) (Pt/TiO(2)), it showed a marked synergistic effect for the photocatalytic hydrogen production compared with GO/TiO(2) and Pt/TiO(2). This indicates that the cheap and abundant carbon material can be a good candidate for an electron attracting reservoir and an auxiliary co-catalyst for the photocatalytic hydrogen production.     

Mesoporous TiO2 nanostructures: a route to minimize Pt loading on titania photocatalysts for hydrogen production

Mesostructured TiO(2) nanocrystals have been prepared using Pluronic F127 as the structure-directing agent. Platinum nanoparticles at different contents (0.1-1.0 wt%) have been photochemically deposited onto the mesoporous TiO(2). TEM investigation of 0.2 wt% Pt/TiO(2) calcined at 450 °C reveals that the TiO(2) particles are quite uniform in size and shape with the particle sizes of TiO(2) and Pt being 10 and 3 nm, respectively. The photocatalytic activities of the Pt loaded TiO(2) have been assessed and compared with those of nonporous commercial Pt/TiO(2)-P25 by determining the rates and the photonic efficiencies of molecular hydrogen production from aqueous methanol solutions. The results show that the amount of hydrogen evolved on Pt/TiO(2)-450 at low Pt loading (0.2 wt%) is three times higher than that evolved on Pt/TiO(2)-P25 and twelve times higher than that evolved on Pt/TiO(2)-350. Despite the BET surface area of the TiO(2)-450 photocatalyst being 3.5 times higher than that of TiO(2)-P25, a 60% smaller amount of the Pt co-catalyst is required to obtain the optimum photocatalytic hydrogen production activity. The reduced Pt loading on the mesoporous TiO(2) will be important both from a commercial and an ecological point of view.     

Furfuraldehyde hydrogenation on titanium oxide-supported platinum nanoparticles studied by sum frequency generation vibrational spectroscopy: Acid-base catalysis explains the molecular origin of strong metal-support interactions

This work describes a molecular-level investigation of strong metal-support interactions (SMSI) in Pt/TiO(2) catalysts using sum frequency generation (SFG) vibrational spectroscopy. This is the first time that SFG has been used to probe the highly selective oxide-metal interface during catalytic reaction, and the results demonstrate that charge transfer from TiO(2) on a Pt/TiO(2) catalyst controls the product distribution of furfuraldehyde hydrogenation by an acid-base mechanism. Pt nanoparticles supported on TiO(2) and SiO(2) are used as catalysts for furfuraldehyde hydrogenation. As synthesized, the Pt nanoparticles are encapsulated in a layer of poly(vinylpyrrolidone) (PVP). The presence of PVP prevents interaction of the Pt nanoparticles with their support, so identical turnover rates and reaction selectivity is observed regardless of the supporting oxide. However, removal of the PVP with UV light results in a 50-fold enhancement in the formation of furfuryl alcohol by Pt supported on TiO(2), while no change is observed for the kinetics of Pt supported on SiO(2). SFG vibrational spectroscopy reveals that a furfuryl-oxy intermediate forms on TiO(2) as a result of a charge transfer interaction. This furfuryl-oxy intermediate is a highly active and selective precursor to furfuryl alcohol, and spectral analysis shows that the Pt/TiO(2) interface is required primarily for H spillover. Density functional calculations predict that O-vacancies on the TiO(2) surface activate the formation of the furfuryl-oxy intermediate via an electron transfer to furfuraldehyde, drawing a strong analogy between SMSI and acid-base catalysis.     

Sn对肉桂醛加氢催化剂Pt/Al2O3的修饰作用

研究了负载型Pt催化剂上肉桂醛加氢反应规律,并对Sn的修饰作用进行了考察.未修饰催化剂Pt/Al2O3上,主要以C=C加氢为主;加入少量Sn修饰剂,肉桂醛加氢活性大幅度提高,而且C=O加氢选择性有所提高.当Sn/Pt摩尔比大于0.8后,虽然C=O加氢选择性仍较高,但加氢活性明显降低.Sn/Pt摩尔比为1的催化剂上,肉桂醛转化率高于96%时,肉桂醇选择性可高达80%.结合XRD与化学吸附等表征结果,表明电子因素和立体因素的综合作用是影响肉桂醛加氢选择性的主要因素.     

An Alkene‐Promoted Borane‐Catalyzed Highly Stereoselective Hydrogenation of Alkynes to Give Z‐ and E‐Alkenes

The stereoselective hydrogenation of alkynes to alkenes is an extremely useful transformation in synthetic chemistry. Despite numerous reports for the synthesis of Z‐alkenes, the hydrogenation of alkynes to give E‐alkenes is still not well resolved. In particular, selective preparation of both Z‐ and E‐alkenes by the same catalytic hydrogenation system using molecular H₂ has rarely been reported. In this paper, a novel strategy of using simple alkenes as promoters for the HB(C₆F₅)₂‐catalyzed metal‐free hydrogenation of alkynes was adopted. Significantly, both Z‐ and E‐alkenes can be furnished by hydrogenation with molecular H₂ in high yields with excellent stereoselectivities. Further experimental and theoretical mechanistic studies suggest that interactions between H and F atoms of the alkene promoter, borane intermediate, and H₂ play an essential role in promoting the hydrogenolysis reaction.     

3 d Transition Metal‐Catalyzed Hydrogenation of Nitriles and Alkynes

Selective hydrogenation of nitriles and alkynes is crucial considering the vast applications of reduced products in industries and in the synthesis of bioactive compounds. Particularly, the late 3d transition metal catalysts (manganese, iron, cobalt, nickel and copper) have shown promising activity for the hydrogenation of nitriles to primary amines, secondary amines and imines. Similarly, semihydrogenation of alkynes to E‐ and Z‐alkenes by 3d metals is adequately successful both via the transfer hydrogenation and by using molecular hydrogen. The emergence of 3d transition metals in the selective synthesis of industrially relevant amines, imines and alkenes makes this protocol more attractive. Herein, we provide a concise overview on the late 3d transition metal‐catalyzed hydrogenation of nitriles to amines and imines as well as semihydrogenation of alkynes to alkenes.     

Effect of transition metals (Cr, Mn, Fe, Co, Ni and Cu) on selective hydrogenation of cinnamaldehyde over Pt/CNTs catalyst

Summary The effect of transition metals (Cr, Mn, Fe, Co, Ni and Cu) on the selective hydrogenation of cinnamaldehyde (CMA) to the corresponding semi-hydrogenated product over Pt/CNTs catalyst has been studied in ethanol at 343 K under 2.0 MPa H₂ pressure. PtNi/CNTs catalyst shows good catalytic activity and selectivity of C=C bond hydrogenation, 68.4% for conversion of CMA and 97.0% for selectivity of hydrocinnamaldehyde (HCMA). PtCo/CNTs catalyst shows good catalytic activity and selectivity of C=O bond hydrogenation, 91.3% for conversion of CMA and 88.2% for selectivity of cinnamylalcohol (CMO).     

Polymer-supported 2,2′-dipyridylmethane: catalytic activity of transition metal complexes in hydrogenations and oligomerizations

The palladium(II) acetate complex of the chelating ligand 2,2′-dipyridylmethane supported on polystyrene-2% divinylbenzene is an efficient catalyst for hydrogenation of alkenes and alkynes. Cyclopentadiene can be reduced with high selectivity to cyclopentene, but no selectivity is observed for the non-conjugated diene 1,5-cyclooctadiene. In the hydrogenation of 3-methylcyclohex-2-en-1-ol only small amounts of ketone are formed as a by-product, in contrast to the reaction catalysed by palladium on charcoal. Nickel(II) complexes of the same ligand catalyze the trimerization of butadiene to 1,5,9-cyclododecatrienes.     

Photocatalytic degradation of 2,4,6-trinitrotoluene

A Pt/TiO2 photocatalyst was used in the photocatalytic degradation of 2,4,6-trinitrotoluene (TNT) under the irradiation of the simulated sunlight. The results show that the destruction of TNT is faster and more complete with the photocatalyst. The photocatalytic degradation of TNT follows first order kinet-ics. The transformation of nitryl groups of TNT molecules into nitrite and nitrate ions may be acceler-ated in the presence of the Pt/TiO2 photocatalyst. Compared with that without the catalyst, the concentration of nitrate ions was improved 32.3 times within 2.5 h.