催化剂Ni/Y2O3上低温乙醇水蒸气重整制氢研究——氢气预还原对催化剂性能的影响

用浸渍－热分解－氢还原法(IHDHR)和浸渍－热分解法(IHD)分别制备了两种纳米尺寸的Ni/Y2O3催化剂，并应用X-光电子能谱、X-射线衍射、BET比表面测试等分析技术对两种催化剂的结构进行了表征和比较。采用固定床反应器对两种催化剂的催化性能进行实验测试。结果表明，氢气预还原与否对该纳米Ni/Y2O3催化剂的催化性能有一定的影响，经过氢气预还原的催化剂对低温乙醇水蒸气重整反应表现出较高的活性和稳定性，250?℃时，乙醇的转化率达到81.9%；320 ℃时，乙醇的转化率达到95.3%，对氢气的选择性为53.6%。对经过氢预还原的Ni/Y2O3催化剂进行了60 h的稳定性测试。     

gamma-1,2-H2SiV2W10O40] immobilized on surface-modified SiO2 as a heterogeneous catalyst for liquid-phase oxidation with H2O2

An organic-inorganic hybrid support has been synthesized by covalently anchoring an N-octyldihydroimidazolium cation fragment onto SiO2 (denoted as 1-SiO2). This modified support was characterized by solid-state 13C, 29Si, and 31P NMR spectroscopy, IR spectroscopy, and elemental analysis. The results showed that the structure of the dihydroimidazolium skeleton is preserved on the surface of SiO2. The modified support can act as a good anion exchanger, which allows the catalytically active polyoxometalate anion [gamma-1,2-H2SiV2W10O40]4- (I) to be immobilized onto the support by a stoichiometric anion exchange (denoted as I/1-SiO2). The structure of anion I is preserved after the anion exchange, as confirmed by IR and 51V NMR spectroscopy. The catalytic performance for the oxidation of olefins and sulfides, with hydrogen peroxide (only one equivalent with respect to substrate) as the sole oxidant, was investigated with I/1-SiO2. This supported catalyst shows a high stereospecificity, diastereoselectivity, regioselectivity, and a high efficiency of hydrogen peroxide utilization for the oxidation of various olefins and sulfides without any loss of the intrinsic catalytic nature of the corresponding homogeneous analogue of I (i.e., the tetra-n-butylammonium salt of I, TBA-I), although the rates decreased to about half that with TBA-I. The oxidation can be stopped immediately by removal of the solid catalyst, and vanadium and tungsten species can hardly be found in the filtrate after removal of the catalyst. These results rule out any contribution to the observed catalysis from vanadium and tungsten species that leach into the reaction solution, which means that the observed catalysis is truly heterogeneous in nature. In addition, the catalyst is reusable for both epoxidation and sulfoxidation without any loss of catalytic performance.     

高活性Co3O4负载单原子Au催化剂室温催化CO氧化

CO低温氧化是多相催化领域研究最多的反应之一.作为简单、典型的探针反应,其不仅具有重要的基础研究价值,而且在环境污染消除等方面也有着非常重要的实际应用价值.金属氧化物如铜锰(Hopcalite)、铜铬复合氧化物以及氧化钴等都具有优异的低温CO氧化活性.然而氧化物催化剂热稳定性低、反复启动性能差、以及对硫化物、水等物质敏感,严重制约了其实际应用.相对而言,负载型贵金属催化剂因具有较高的CO氧化活性、反应稳定性以及热稳定性而受到关注.但是贵金属价格昂贵、资源稀少,使其持续应用面临严峻挑战.为了提高贵金属利用效率、降低贵金属使用量,在负载型贵金属催化剂中,贵金属多以纳米尺度分散于高比表面载体上.由于多相催化一般在纳米粒子表面发生,只有表面金属原子能够接触到反应物,因而贵金属原子利用率仍然有待提高.最近本课题组成功开发以原子级分散的单原子催化剂并提出“单原子催化”的概念.后续研究以及其他研究人员相继证明氧化物负载贵金属单原子具有高活性和/或不同于纳米粒子的反应性能,表明开发单原子催化剂是最大化贵金属利用效率、降低贵金属用量的可行途径.对于CO氧化而言,目前普遍认为负载Au催化剂具有最高活性.然而负载Au单原子催化剂是否具有活性仍存争议：理论计算表明氧化物负载Au单原子催化剂具有很好的活性,但是缺少实验证据;目前已有一些氧化物负载Au正价离子催化剂的报道,结果也都表明Au单原子活性远低于纳米粒子或纳米团簇.最近本课题组发现氧化铁负载Au单原子不仅具有与Au纳米粒子相当的单位活性位(TOF)活性而且具有更高的单位金属重量(反应速率)活性以及非常高的反应稳定性.本文将载体拓展到氧化钴,开发了具有更高活性的氧化钴负载Au单原子催化剂, Au负载量仅为0.05 wt%即可在室温条件下实现CO完全转化. Co3O4载体用Co(NO3)3与Na2CO3通过共沉淀法制备,400 oC焙烧.然后通过简单的沉淀吸附法制备Co3O4负载Au单原子催化剂(Au1/Co3O4),确保Au单原子能够分散于载体的表面.具有原子分辨率的球差校正高分辨电镜照片显示Au原子确实以单原子形式分散于载体上.催化剂在第一个循环中活性并不非常高,但是在第二个循环中活性提高非常明显,可以在室温条件下实现CO全转化.为了弄清楚活性提高的原因,我们用惰性气体(He)、氧化性气体(5%O2/He)以及还原性气体(5%CO/He)对催化剂进行了热处理,但是活性提高并不明显.由此推断催化剂是在第一个循环反应过程中发生了某些变化,导致活性显著提高.空白载体实验表明Co3O4载体本身虽然具有反应活性,但是远不如负载少量Au原子活性高,表明Au原子或Au原子与载体一起起到高活性的作用.稳定性研究表明该催化剂在室温条件下容易失活,但经惰性气体或氧化气体处理后活性可恢复,表明不是结构性失活而是可逆失活,说明单原子非常稳定.     

Peroxophosphotungstate held in an ionic liquid brush: an efficient and reusable catalyst for the dihydroxylation of olefins with H2O2 in neat water

A reusable heterogeneous catalytic assembly of [PO₄{WO(O₂)₂}₄]^3? held in an ionic liquid brush was synthesized and an environmentally friendly procedure was developed for the dihydroxylation of several olefins with 30 wt% H₂O₂. These reactions were conducted in neat water under mild conditions without any organic co‐solvent or other additive. Several factors that affect the dihydroxylation were investigated in detail. The catalyst is easily recovered after the reaction via simple filtration, and can be reused at least eight times without a noticeable loss of activity. The experimental results demonstrate that this dihydroxylation process has no apparent scale‐up effect. Copyright © 2014 John Wiley & Sons, Ltd.     

Interplay between defect structure and catalytic activity in the Mo(10-x)V(x)O(y) mixed-oxide system

The Mo(10-x)V(x)O(y) solid-solution systems (0≤x≤10) were studied by electron paramagnetic resonance spectroscopy. The results show the existence of paramagnetic vanadyl VO(2+) species, whose concentration becomes maximal for Mo(5)V(5)O(y·). A quantitative analysis of the [VO(2+)] concentration as a function of the Mo/V ratio allows it to characterize the prevailing defect chemistry in the Mo(10-x)V(x)O(y) system. In this respect, the semi-conducting properties of Mo(10-x)V(x)O(y) are p-type in an interval of Mo(9)V(1)O(y)-Mo(5)V(5)O(y) and switch into n-type because of the conduction electrons in a composition range of Mo(5)V(5)O(y)-Mo(1)V(9)O(y). Highest catalytic activity is obtained when vanadium acts as an acceptor center and oxygen vacancies ν(··)(O) are formed for reasons of charge compensation. In addition to the surface, ν(··)(O) and VO(2+) centers in the bulk have to be considered too for heterogeneous catalysis.     

Synergies between bio- and oil refineries for the production of fuels from biomass

As petroleum prices continue to increase, it is likely that biofuels will play an ever-increasing role in our energy future. The processing of biomass-derived feedstocks (including cellulosic, starch- and sugar-derived biomass, and vegetable fats) by catalytic cracking and hydrotreating is a promising alternative for the future to produce biofuels, and the existing infrastructure of petroleum refineries is well-suited for the production of biofuels, allowing us to rapidly transition to a more sustainable economy without large capital investments for new reaction equipment. This Review discusses the chemistry, catalysts, and challenges involved in the production of biofuels.