Generation of Basic Centers in High-Silica Zeolites and their Application in Gas-Phase Upgrading of Bio-Oil
作者:Tobias C. Keller、Elodie G. Rodrigues、Javier Pérez-Ramírez
DOI:10.1002/cssc.201301382
日期:2014.6
High‐silica zeolites have been reported recently as efficientcatalysts for liquid‐ and gas‐phase condensation reactions because of the presence of a complementary source of basicity compared to Al‐rich basic zeolites. Herein, we describe the controlled generation of these active sites on silica‐rich FAU, BEA, and MFI zeolites. Through the application of a mild base treatment in aqueous Na2CO3, al
最近,由于与富铝碱性沸石相比,存在补充的碱性来源,因此高硅沸石已成为液相和气相缩合反应的有效催化剂。本文中,我们描述了在富含二氧化硅的FAU,BEA和MFI沸石上这些活性位点的受控生成。通过在Na 2 CO 3水溶液中应用温和的碱处理,在沸石内产生碱金属配位缺陷,而充分保留了多孔性。所得的催化剂被用于在673 K下丙醛的气相缩合反应中,作为催化裂解热解油的模型反应,与未改性的沸石相比,其活性提高了20倍。这些新位点的适度碱度导致其抗焦炭性能优于传统的碱催化剂(如CsX和MgO),并且对冷凝路径具有可比的活性和出色的选择性。通过战略性的酸和碱处理以及魔角旋转NMR光谱学,研究了活性位点的性质,这支持了以甲硅烷氧基位点为基本中心的理论。
Hierarchical high-silica zeolites as superior base catalysts
作者:Tobias C. Keller、Stéphane Isabettini、Danny Verboekend、Elodie G. Rodrigues、Javier Pérez-Ramírez
DOI:10.1039/c3sc51937f
日期:——
For more than four decades, the design of zeolite base catalysts has relied on the application of aluminium-rich frameworks exchanged with alkali metal cations (preferably Cs+). However, moderate activity associated with access and diffusion limitations, and high manufacturing costs associated with high caesium content (typically over 30%) have hampered their industrial implementation so far. Herein, we have discovered that high-silica USY zeolites outperform their Al-rich counterparts in a variety of base-catalysed reactions of relevance in the fine chemical industry, as well as in the upgrading of biofuels. The benefits of this class of materials are amplified upon the alleviation of diffusion constraints through the introduction of a network of intracrystalline mesopores by post-synthetic modification. For example, the resulting cation-free hierarchical USY provides an up to 30-fold Knoevenagel condensation activity compared to the benchmark Cs–X, and similar observations were made upon application in liquid-phase (nitro)aldol reactions. Moreover, in the gas-phase aldol condensation of propanal, high-silica zeolites provide superior activity, selectivity, and lifetime compared to caesium-containing zeolites and even a strong solid base such as MgO. We decouple the complex interplay between mesoporosity and intrinsic zeolitic properties such as crystallinity, and quantify the increase in catalyst effectiveness upon hierarchical structuring as a function of reactant size. The obtained results are a major step to resolve the drawbacks of zeolites catalysis and thereby revitalise their potential for industrial application.
Condensation and esterification reactions of alkanals, alkanones, and alkanols on TiO2: Elementary steps, site requirements, and synergistic effects of bifunctional strategies
作者:Shuai Wang、Konstantinos Goulas、Enrique Iglesia
DOI:10.1016/j.jcat.2016.05.026
日期:2016.8
6-di-tert-butylpyridine, pyridine, CO2, and propanoic acid during catalysis showed that Lewisacid–base site pairs of moderate strength mediate enolate formation steps via concerted interactions with the α-H atom and the enolate moiety at transition states. The resulting site-counts allow rigorous comparisons between theory and experiments and among catalysts on the basis of turnover rates and activation
TiO 2催化的C 3含氧化合物(丙醛,丙酮)缩合反应的速率和选择性受到副反应,失活和热力学瓶颈的普遍影响。作为与TiO 2的物理混合物形式存在的H 2与Cu功能一起,通过清除不饱和中间体来规避此类障碍。它们还通过快速相互转化使链烷醇和链烷烃/链烷酮等同于反应物,同时通过使不稳定的半缩醛脱氢而实现酯化转化。含氧化合物与新的C C和C形成分子O键和较少的O原子以稳定的速率和选择性几乎完成了完全转化。动力学,同位素和理论方法表明,速率受到羰基反应物从α-CH裂解形成烯醇盐中间体的限制,该中间体与另一种羰基化合物进行C C偶联形成α,β-不饱和含氧化合物或与烷醇形成半缩醛,通过形成氢氧根-烷烃对的中间H位移,形成新的C O键。用2,6-二叔丁基吡啶,吡啶,CO 2滴定和丙酸在催化过程中显示,中等强度的路易斯酸-碱位点对通过过渡态与α-H原子和烯醇盐部分的协同相互作用介导烯醇盐形成步骤。产生的位点
Hydroxyapatite, an exceptional catalyst for the gas-phase deoxygenation of bio-oil by aldol condensation
作者:E. G. Rodrigues、T. C. Keller、S. Mitchell、J. Pérez-Ramírez
DOI:10.1039/c4gc01432d
日期:——
Hydroxyapatites displaying high surface concentrations of calcium exhibit exceptional performance in the gas-phase condensation of propanal, a model substrate for the intermediate deoxygenation of biocrude.
表面钙浓度高的羟基磷灰石在生物原油中间体脱氧化的模型底物丙醛的气相凝聚中表现出卓越的性能。
Preparation of aliphatic carbonyl compounds
申请人:BASF Aktiengesellschaft
公开号:US04270006A1
公开(公告)日:1981-05-26
Aliphatic carbonyl compounds are prepared by an aldol condensation of carbonyl compounds R.sup.1 --CH.sub.2 --CO--R.sup.2 (I; R.sup.1 and R.sup.2 =H or C.sub.1 -C.sub.8 -alkyl) in the presence of hydrogen and of a catalyst which has both condensing and hydrogenating properties, by using a catalyst system wherein the active components are from 1 to 90 percent by weight of a noble metal of group VIII of the periodic table and from 10 to 99 percent by weight of an oxide or salt of a rare earth metal, or of a mixture of different oxides and/or salts of rare earth metals.