多相催化的三個層面

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前言：

1. Dumesic等人在Handbook of heterogeneous catalysis一書中將催化研究分為材料製備(materials)，催化劑性能(catalytic performance)和催化機理論述(elucidation)這三個層面，並認為催化機理的理解是引領先進催化劑設計的最關鍵的一步。

2. 化石能源的日益枯竭帶來了能源與材料危機，化學家們嘗試著從不同角度來解決這個問題，包括太陽能與氫能（水分解，光電催化以及電池等）, 生物質能源，低鏈烷烴的利用（甲烷偶聯/芳構化，丙烷脫氫等）等。

今天，剛好借用最近發表的幾篇文章，展示下目前多相催化研究的部分方向與特點。（僅代表個人觀點，歡迎大家留言討論）

第一篇：催化材料的製備(納米材料合成)，代表催化研究的第一個層面，當然也是很重要的一個方面。不誇張的說，先進催化材料的製備是催化化學的基礎。

本文選自Science，關注於納米晶的可控合成。

一句話評述：室溫下，採用Cu2O納米晶為母體，離子交換的方式得到了其他各種有特色的納米晶材料。

材料的特點：半導體材料，納米晶 用途：半導體相關用途包括光催化等

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，對於催化機理的研究是基於大量催化劑性能的異同，經總結設計之後通過相應手段得到的。催化性能將催化材料和催化機理連接在一起，當然也是工業應用時最關注的一個方面。

本文選自Applied catalysis B: Enviromental,關注於生物質轉化。

一句話評述：Cu,Sn的引入可以顯著提高Ni/Al2O3催化脂類加氫脫氧制柴油的性能，這可能是因為Cu可以增加Ni的還原性，抑制裂化和積碳等。

備註：生物質的加氫脫氧是生物質能源利用的一個主要方向，有興趣的同學可以關注下。

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，選自J.Catal.,關注低鏈烷烴的利用(丙烷脫氫).

一句話評述：PtIn/Mg(Al)O-pX催化劑在催化丙烷脫氫時，載體Mg(Al)O的製備條件-共沉澱時的PH-對催化性能有很大的影響。

備註：丙烷在天然氣中佔有較高的比例，但目前我國對於天然氣中丙烷的使用多用於直接燃燒。從資源有效利用的角度考慮，鑒於其脫氫產物丙烯是非常重要的工業原料，因此丙烷脫氫制丙烯受到人們的關注

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：催化機理研究。催化機理的研究其實也分為很多步，包括催化劑結構與催化性能之間的關係，催化反應由哪些基元反應構成，哪一步是決速步驟，催化反應過渡態的確定以及催化劑如何影響過渡態，如何根據催化機理設計先進催化劑等等。嚴格意義上來說，目前真正搞得很清楚的催化反應很少。已經比較清楚的，有代表性的是2007年諾貝爾獎得主Ertl研究的Pt表面的CO氧化。

本文選自J. Am. Chem. Soc., 關注於水氧化反應，通訊作者是哈佛大學的Nocera，做OER的同學想來不會陌生。

一句話評述：採用DEMS(Differentialelectrochemical mass spectrometry), 17O NMR等手段研究了Co氧化物催化劑Edge Site的反應特性，這對解釋OER反應機理以及關聯均相（分子催化劑）與多相催化劑(氧化物，氫氧化物催化劑)提供了非常有利的證據。

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：過段時間，我會將OER催化劑的大致分類進行總結，希望能夠加深大家對OER催化劑的了解，敬請期待。

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