催化甘油脱水氧化连续反应的酸碱位共存粘土基催化剂研究

The preparation of well-designed inorganic solid catalysts combining acidic sites and basic metal oxide sites is a primary issue for the novel process of heterogeneously catalytic consecutive dehydration-oxidation of glycerol to produce acrylic acid. Based on previous studies on the catalysts for catalytic dehydration of glycerol and catalytic oxidation of glycerol, the present proposal suggests an innovative novel methodology for the preparation of coexisting acid-base solids catalysts from the combination of anionic clay layers and cationic clay layers by means of delamination and then the re-assembly, following by in situ transformation of the anionic Cu-Al-Mg clay nanolayers in the interlayer space of acidic saponite clay into basic Cu-Al-Mg oxides. In this way, a type of solid catalysts with coexisting acidic and basic sites for catalytic dehydration and oxidation of glycerol can be obtained. In particular, physicochemical approaches to the delamination and re-assembly of saponite layers and anionic Cu-Al-Mg clay layers in a layer-by-layer way will be developed and the formation mechanism will be examined. And the effects of the composition, the layer charge density, the size of layers of the layered precursors on the amount, type, distribution of surface acidity and basicity, microstructure, chemical bonds and catalytic performances of the resulting catalysts will be investigated. Emphasis will be put on revealing the formation mechanism, the tuning methods and principles of acidic sites from saponite layers and basic sites from Cu-Al-Mg oxides in the resulting catalysts. The well-matched recation conditions for the consecutive dehydration-oxidation of glycerol to produce acrylic acid.the will be identified. For such catalysts, the correlation among the preparation factors, the structural parameters and the catalytic properties in the heterogeneously catalytic consecutive dehydration-oxidation of glycerol will be disclosed and the inherent reasons will be theoretically elaborated. To our knowledge, such a preparation route to the catalysts with coexisting acidic and basic sites for catalytic oxidation and dehydration of glycerol and scientific investigation therein have not yet been reported at home and abroad. It belongs to a multidisciplinary topic involving in catalysis, clay minerals and the processing of bioresource-based chemical feedstocks.

设计制备同时具有酸性位和碱性金属氧化物位的无机固体催化剂，是研发催化甘油脱水氧化连续反应制丙烯酸新过程中的关键问题。基于申请者对甘油脱水和氧化反应的前期研究，项目提出Cu-Al-Mg碱性阴离子粘土和酸性皂石阳离子粘土片层解离再组装的新思路，在酸性皂石片层间原位生成Cu-Al-Mg碱性复合氧化物，制成酸位和碱位共存的固体材料，表征认识碱、酸位的形态、组成、形成机制和催化甘油脱水氧化行为；主要研究调控片层解离和组装的方法及作用原理，考察前驱体片层组成、电荷密度、尺度等因素对催化剂中酸性位和碱性复合氧化物活性位数量、类型、分布、微结构、键合状态及催化性的影响；重点揭示催化剂中皂石片层酸性和碱性复合氧化物活性位的调控机制，认识其催化甘油脱水氧化连续反应生成丙烯酸的匹配条件及内在原因，弄清制备、结构与催化作用特征之间的相互关系。该思路和内容在国内外尚未有报道，系催化、粘土和生物基化学品化工交叉研究。

催化甘油脱水氧化连续反应生成丙烯酸的新反应系可持续化的绿色化学新工业过程，其核心科学和技术问题在于催化剂的研究开发。项目探索制备了具有酸性位和碱性金属氧化物位的多功能的无机固体催化剂及研究了其催化甘油脱水氧化作用机制。实验制备了多个系列的多功能催化剂，采用的粘土矿物主要有蒙脱石、合成皂石和海泡石粘土矿物等，采用的碱性氧化物主要有氧化镁、氧化铜及相应的阴离子粘土矿物等；采用了X射线晶体衍射、X射线荧光光谱、扫描电子显微镜、热重分析、N2吸附-脱附等温线分析、NH3程序升温脱附分析、傅里叶变换红外光谱和吡啶吸附的原位红外光谱等表征了催化剂样品；采用连续流动固定床反应器评价了催化剂的性能。实验考察了前驱体片层组成、尺度、酸活化处理以及负载铜、钨、钒、杂多酸等对催化剂上活性位数量、类型、分布、微结构、键合状态及催化性能的影响，讨论认识了催化剂活性位实质和调控机制。结果发现，采用盐酸、硫酸、磷酸、醋酸等均可对粘土矿物进行酸活化，采用不同酸和酸浓度等，可以调变粘土矿物片层粒度和形貌、表面酸性等，从而可以调变相应的催化剂的催化甘油气相脱水氧化反应的性能。酸性粘土催化剂催化下的甘油转化反应，主要发生脱水反应且主要产物是丙烯醛和羟基丙酮，丙烯醛的生成与B酸位量及其强度相关度高。在反应温度为320 ℃，空气流速为20ml/min，进料为15 wt.% 甘油的反应条件下，2mol/L盐酸改性的海泡石催化剂的催化效果相对最佳，甘油的转化率为92.9%，丙烯醛的选择性为59.4%，丙烯酸选择性3.8%。研究发现，要提高丙烯酸的选择性，需要负载铜、钨、钒等。磷酸改性的蒙脱石负载铜、钨、钒催化剂的具有催化脱水氧化活性，但与铜、钨、钒的晶形、数量和分布密切相关；如WOx负载在蒙脱石表面上以[WO5/WO6](B酸位)、[WO4]和单斜晶系WO3相(L酸位)等多种形式存在，当钨负载量从12 wt%增至16wt%， 孤立的单斜晶系WO3晶粒增多；蒙脱石上负载WOx能够调节催化剂的酸强度、酸量、酸位类型和相应的氧化活性。研究也发现，各催化剂尚存在积碳和易失活问题，亟待后续科学研究解决。实验结果和理论认识对推进催化甘油脱水氧化连续反应的实现工业化具有重要价值。