生物质衍生物“平台分子”增值转化的多相催化研究

Increasing concern on the depletion of oil and other fossil resources has stimulated great interest on seeking sustainable technologies for chemicals production from renewable bio-resources. This proposal aims to develop toolboxes for chemo-selective upgrading of biomass-derived platform molecules (glycerol, lactic acid and xylitol) to value-added chemicals using heterogeneous selective dehydration and oxidation catalysis. One aspect of this proposed project will be devoted to understand the chemistry of acid-base catalysis for selective gas-phase dehydration of glycerol and lactic acid, with acrolein and acrylic acid being the desired products, respectively; suitable solid catalysts with desirable acidity or basicity will be developed towards water-tolerant, highly efficient catalysis. A specific attention will be paid on identifying techniques that can be applied to characterize the acid-base properties of solid catalysts with the presence of different amounts of water (steam). Another aspect is devoted to explore and elucidate the nature of active sites on supported metallic catalysts for selectivity control of the oxidation reactions of glycerol, lactic acid and xylitol. Our recently developed M-on-Au nanostructures (M^Au, M = Pd，Pt，Ru and Rh), with varying dispersion states of M and M-Au interaction, will be included in the catalysts for the oxidation catalysis study. Correlations between of the catalytic performance (activity, selectivity and catalytic stability) and the dispersion state of the M entities and/or M-Au interactions will be established. A particular research interest will be put on identifying catalytic nanostructures that would precisely activate a specific functional group or its associated carbon atom for catalytic oxidation, making the process specific for a target product. Also, competitive oxidation of two alcohols (mono-alcohol or diols) is proposed to be performed to discriminate and group metallic surface sites specific for catalyzing the oxidation towards a definite product. The knowledge gained from these competitive oxidation reaction measurements will then be used for catalysis design and applied to generate mechanistic understanding of the selective oxidation catalysis. The results gained in this proposed work would have important implication in developing highly performing catalysts and catalytic processes for chemicals prodcution from renewables.

围绕生物质平台分子甘油、乳酸和木糖醇的催化活化和定向增值转化，进行固体酸碱催化脱水反应以及负载型金属催化氧化反应的选择性多相催化研究。具体针对甘油制丙烯醛、乳酸制丙烯酸的气相脱水反应，探索发展评价含水气氛中固体表面酸碱性质的物理化学方法，研究相关活性位本质、酸碱催化机理和催化剂失活规律，发现和创造耐水性高效固体酸碱催化剂；以研发甘油、乳酸和木糖醇选择氧化制取高附加值化学品催化新技术为目标，研究纳米结构M^Au（M=Pd，Pt，Ru或Rh）催化剂体系M分散状态和M-Au相互作用与甘油、乳酸和木糖醇氧化反应的活性、选择性和稳定性的关系，发现和研制能够“精准选择”多元醇（甘油、木糖醇）或多基团分子（乳酸）“反应位置”的纳米结构催化剂，阐明这些平台分子的催化活化与定向氧化反应机理。本项目可望发展固体催化剂的设计制备思想、并为其它相关选择性催化剂的改造、优化和创新提供基础数据和技术积累。

本课题围绕生物质衍生物“平台分子”增值转化的多相催化进行系统性基础，取得以下特色性工作成果：.1) 研究了碱金属离子交换沸石（包括不同维数、孔道尺寸以及笼尺寸，不同硅铝比等）以及系列羟基磷灰石对乳酸（LA）脱水制丙烯酸（AA）反应的催化作用规律，发明了性能优异的ZSM-5催化剂，阐释了其中的酸碱协同催化作用，获得了反应的动力学参数和速率方程，提出了相应表面催化机理；发现对LA制AA有效的催化剂也对用乳酸酯替代LA制取AA具备良好的催化性能，但是乳酸酯分子必须先发生酸催化水解转变为LA（或表面乳酸盐）中间物，后者再在酸碱协同催化作用下才能脱水生成AA，揭示了由乳酸酯制取AA是酸催化水解与酸碱协同脱水两个表面催化过程“串联”的结果。.2) 以Ta2O5H2O-350为催化剂，研究了甘油脱水反应的动力学规律，建立了相应动力学方程，测定了相关动力学参数，提出了可能的决速步骤以及表面基元步骤系列（机理）。.3) 以-Al2O3和SiO2-Al2O3催化肉桂醛-异丙醇和乙酰丙酸（脂）异丙醇的MPV反应中，通过原位选择性毒化，甄别了催化剂表面B酸位（BAS）与L酸位（LAS）的催化功能，证实表面LAS是催化MPV反应的活性位。.4) 利用3,3-二甲基-1-丁烯异构、异丙醇脱水等多个探针反应，在典型固体酸碱催化剂上观测到水汽可导致以下表界面现象：一些LAS被毒化，一些LAS转变成新的BAS、以及一些原有BAS的酸强度被弱化，并据此探索提出评价和测定含水体系固体表面酸性的反应化学新方法。.5) 发现水溶液中的NaOH即可充当醇类氧化反应的均相催化剂，确立了NaOH催化甘油、乙二醇和乙醇氧化反应的活性次序，提出了可能的反应机理；在有Au催化剂共存时，NaOH主要起助催化剂作用，使主要产物由无碱时的DHA变为甘油酸。因此，载体材料的表面酸碱性也是有效控制Au催化剂上甘油氧化反应选择性的重要方面。.6) 发现在负载型Au、Pt和Pd等贵金属催化剂表面存在着相互独立的选择氧化伯碳醇与选择氧化仲碳醇的活性位，建立了在无碱条件下研究水中两种醇分子（如伯碳醇与仲碳醇）竞争氧化反应的实验方法。..前四条内容丰富和发展了固体酸碱催化化学，可望为进一步研发相关高性能催化剂提供启示与指导作用；第五条发现有望为完善对甘油选择氧化机理的认识、发展更有效的选择性催化剂有所贡献；最后一项工作有可能成为