文献精选-2016-3-21-多相催化的三个层面
前言：
1. Dumesic等人在Handbook of heterogeneous catalysis一书中将催化研究分为材料制备(materials)，催化剂性能(catalytic performance)和催化机理论述(elucidation)这三个层面，并认为催化机理的理解是引领先进催化剂设计的最关键的一步。
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2. 化石能源的日益枯竭带来了能源与材料危机，化学家们尝试着从不同角度来解决这个问题，包括太阳能与氢能（水分解，光电催化以及电池等）, 生物质能源，低链烷烃的利用（甲烷偶联/芳构化，丙烷脱氢等）等。
今天，刚好借用最近发表的几篇文章，展示下目前多相催化研究的部分方向与特点。（仅代表个人观点，欢迎大家留言讨论）
第一篇：催化材料的制备(纳米材料合成)，代表催化研究的第一个层面，当然也是很重要的一个方面。不夸张的说，先进催化材料的制备是催化化学的基础。
本文选自Science，关注于纳米晶的可控合成。
一句话评述：室温下，采用Cu2O纳米晶为母体，离子交换的方式得到了其他各种有特色的纳米晶材料。
材料的特点：半导体材料，纳米晶 用途：半导体相关用途包括光催化等
The crystal structure of ionic nanocrystals (NCs) is usually controlled through reaction temperature, according to their phase diagram. We show that when ionic NCs with different shapes, but identical crystal structures, were subjected to anion exchange reactions under ambient conditions, pseudomorphic products with different crystal systems were obtained. The shape-dependent anionic framework (surface anion sublattice and stacking pattern) of Cu2O NCs determined the crystal system of anion-exchanged products of CuxS nanocages. This method enabled us to convert a body-centered cubic lattice into either a face-centered cubic or a hexagonally close-packed lattice to form crystallographically unusual, multiply twinned structures. Subsequent cation exchange reactions produced CdS nanocages while preserving the multiply-twinned structures. A high-temperature stable phase such as wurtzite ZnS was also obtained with this method at ambient conditions
第二篇：催化性能研究。一般而言，对于催化机理的研究是基于大量催化剂性能的异同，经总结设计之后通过相应手段得到的。催化性能将催化材料和催化机理连接在一起，当然也是工业应用时最关注的一个方面。
本文选自Applied catalysis B: Enviromental,关注于生物质转化。
一句话评述：Cu,Sn的引入可以显著提高Ni/Al2O3催化脂类加氢脱氧制柴油的性能，这可能是因为Cu可以增加Ni的还原性，抑制裂化和积碳等。
备注：生物质的加氢脱氧是生物质能源利用的一个主要方向，有兴趣的同学可以关注下。
The ability of Cu and Sn to promote the performance of a 20% Ni/Al2O3 catalyst in the deoxygenation of lipids to fuel-like hydrocarbons was investigated using model triglyceride and fatty acid feeds, as well as algal lipids. In the semi-batch deoxygenation of tristearin at 260 oC a pronounced promotional effect was observed, a 20% Ni–5% Cu/Al2O3 catalyst affording both higher conversion (97%) and selectivity to C10–C17 alkanes (99% of liquid product) in comparison with unpromoted 20% Ni/Al2O3(27% conversion and 87% selectivity to C10–C17). In the same reaction at 350 oC,a 20% Ni–1% Sn/Al2O3 catalyst afforded the best results,giving yields of C10–C17 and C17 of 97% and 55%, respectively, which contrasts with the corresponding values of 87% and 21% obtained over 20% Ni/Al2O3.Equally encouraging results were obtained in the semi-batch deoxygenation of stearic acid at 300 oC, in which the 20% Ni–5% Cu/Al2O3 catalyst afforded the highest yields of C10-C17 and C17. Experiments were also conducted at 260 oC in a fixed bed reactor using triolein – a model unsaturated triglyceride – as the feed. While both 20% Ni/Al2O3 and 20% Ni-5% Cu/Al2O3 achieved quantitative yields ofdiesel-like hydrocarbons at all reaction times sampled, the Cu-promoted catalyst exhibited higher selectivity to longer chain hydrocarbons, a phenomenon which was also observed in experiments involving algal lipids as the feed.Characterization of fresh and spent catalysts indicates that Cu enhances there ducibility of Ni and suppresses both cracking reactions and coke-induced deactivation.
第三篇：催化性能研究，选自J.Catal.,关注低链烷烃的利用(丙烷脱氢).
一句话评述：PtIn/Mg(Al)O-pX催化剂在催化丙烷脱氢时，载体Mg(Al)O的制备条件-共沉淀时的PH-对催化性能有很大的影响。
备注：丙烷在天然气中占有较高的比例，但目前我国对于天然气中丙烷的使用多用于直接燃烧。从资源有效利用的角度考虑，鉴于其脱氢产物丙烯是非常重要的工业原料，因此丙烷脱氢制丙烯受到人们的关注
PtIn/Mg(Al)O-pX catalysts were prepared with co-precipitation method at different pH values (X = 6–12), with the aim of investigating the effect of pH value on their catalytic performance for the propane dehydrogenation reaction. It was found that the co-precipitation pH value could strongly influence the crystalline phase, the specific surface area, the surface morphology, the distribution of surface acidity, the reduction properties of the metal phase, the surface chemical state, the distribution of metal particles, and coke formation, giving rise to different catalytic performance. All the results reveal that the catalyst prepared at pH8 shows the best catalytic performance; it possesses the primary crystal phase of periclase (MgO) and the highest specific surface area of support, the lowest fraction of strong acidic sites and In0 species, the strongest interaction between the metal phase and support, the highest Pt dispersion (41.6%), the best distribution of Pt particles with the smallest Pt particle size (1.8 nm),and the lowest coke amount. Furthermore, the highest once-though yield of 0.37 mol propylene can be obtained over PtIn/Mg(Al)O-p8, in which 0.60 mol propane is consumed in a whole dehydrogenation reaction period(28 h).
第四篇：催化机理研究。催化机理的研究其实也分为很多步，包括催化剂结构与催化性能之间的关系，催化反应由哪些基元反应构成，哪一步是决速步骤，催化反应过渡态的确定以及催化剂如何影响过渡态，如何根据催化机理设计先进催化剂等等。严格意义上来说，目前真正搞得很清楚的催化反应很少。已经比较清楚的，有代表性的是2007年诺贝尔奖得主Ertl研究的Pt表面的CO氧化。
本文选自J. Am. Chem. Soc., 关注于水氧化反应，通讯作者是哈佛大学的Nocera，做OER的同学想来不会陌生。
一句话评述：采用DEMS(Differentialelectrochemical mass spectrometry), 17O NMR等手段研究了Co氧化物催化剂Edge Site的反应特性，这对解释OER反应机理以及关联均相（分子催化剂）与多相催化剂(氧化物，氢氧化物催化剂)提供了非常有利的证据。
Differential electrochemical mass spectrometry (DEMS)analysis of the oxygen isotopologues produced by 18O-labeled Co-OEC in H216Oreveals that water splitting catalysis proceeds by a mechanism that involvesdirect coupling between oxygens bound to dicobalt edge sites of Co-OEC. Theedge site chemistry of Co-OEC has been probed by using a dinuclear cobalt complex.17O NMR spectroscopyshows that ligand exchange of OH/OH2 at Co(III) edge sites is slow, whichis also confirmed by DEMS experiments of Co-OEC. In borate (Bi) and phosphate (Pi) buffers, anionsmust be displaced to allow water to access the edge sites for an O–O bondcoupling to occur. Anion exchange in Pi isslow, taking days to equilibrate at room temperature. Conversely, anionexchange in Bi is rapid (kassoc = 13.1 ± 0.4 M–1 s–1 at 25 °C), enabled by facile changes in boroncoordination. These results are consistent with the OER activity of Co-OEC in Bi and Pi. The Pi bindingkinetics are too slow to establish a pre-equilibrium sufficiently fast toinfluence the oxygen evolution reaction (OER), consistent with the zero-orderdependence of Pi on the OER current density; in contrast,Bi exchange is sufficiently facile suchthat Bi has an inhibitory effect on OER.These complementary studies on Co-OEC and the dicobalt edge site mimic allowfor a direct connection, at a molecular level, to be made between themechanisms of heterogeneous and homogeneous OER.
友情提示：过段时间，我会将OER催化剂的大致分类进行总结，希望能够加深大家对OER催化剂的了解，敬请期待。
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