LaxCe1-xNiO3催化剂上甘油水蒸气重整制氢的本征动力学和机理研究

Steam reforming of glycerol is an efficacious approach for the production of hydrogen as biomass comparing with tridational petrochemical resources. The study on kinetics and mechanism of reaction is helpful for the design of new catalysts, optimization of catalytic conditions, and enlargement of this reforming reaction. However, there are only a few kinetic studies on the steam reforming of glycerol. Furthermore, these studies did not eliminate the effects of transfer of heat or mass, or side reactions on the major reaction. Nor were the kinetic studies on a single metal active site. So far, all the present kinetic studies only gave an overall non-intrinsic kinetics on a total catalyst. Previously, the applicant has already studied the steam reforming of glycerol over LaxCe1-xNiO3 catalysts. In this application, the applicant will investigate the intrinsic kinetic parameters and mechanism of the overall reaction and elementary steps of the steam reforming of glycerol on a single Ni active site of LaxCe1-xNiO3 catalysts by steay and unsteady kinetic methods and by spectral methods, giving reaction rates, reaction turnover frequencies, reaction orders, activation energies, rate-determing step, and the active intermediates during the reaction. And the effects of the size of Ni nano particles and the additive La2O3 or CeO2 on the kinetics and mechanism will also be studied. This study will setup a kinetic model and help us to understand how this reforming reaction is performing on the Ni active sits of LaxCe1-xNiO3 catalysts. This research will provide direct and theoretical basis to design the component of catalysts, optimize the reaction temperature and enlarge this reforming reaction.

甘油水蒸气催化重整制氢作为生物质制氢代替传统石化资源制氢将是一种有效途径。目前，国际上甘油水蒸气重整反应的动力学研究很少，研究中未排除传质、传热和副反应的影响，也未研究单个活性位上的动力学，是催化剂上总包反应的非本征动力学过程。基于申请人前期工作中对LaxCe1-xNiO3催化剂上甘油水蒸气重整反应制氢的催化研究，本申请拟采用稳态和脉冲动力学方法、原位光谱等表征方法，研究系列LaxCe1-xNiO3催化剂Ni活性位上甘油水蒸气重整的总包和基元反应的本征动力学和机理，包括反应的速率、级数、转化频率、活化能、决速步和中间活性物种等。研究Ni颗粒尺寸效应和助剂La2O3和CeO2对动力学和机理的影响。理解在LaxCe1-xNiO3催化剂上甘油水蒸气重整反应的分子机理，建立甘油水蒸气重整反应制氢的动力学模型。为设计催化剂组成、调变活性组分含量、优化反应温度和大规模生产提供直接数和理论依据。

在此部分工作中，通过不同制备条件选取了热力学控制反应条件下的最佳催化剂。研究了催化剂La0.7Ce0.3NiO3上的甘油蒸气重整反应动力学，在温度范围475 ℃到525 ℃之间以及水与甘油比例为15 ≤ STGR ≤ 23的情况下。基于幂律模型对动力学参数进行分析H2O、CO2或H2的反应级数。甘油的表观反应级数以及表观反应活化能分别是0.37和55.0 kJ mol-1。甘油水蒸气重整的机理是水与甘油在La0.3Ce0.7Ni-Al2O3催化剂上竞争解离生成氢，催化剂表面被水和甘油初次解离的活性物种钝化。催化剂表面被钝化后，此时微观重整反应动力学的活化能为27.25 kJ/mol，指前因子为1.271。脉冲动力学研究考察Ni粒度对甘油蒸汽重整动力学的影响，活化能随Ni颗粒度的大小变化为8%>4%>2%>10%>6%，指前因子的顺序为8%>4%>10%>2%>6%。两者的基本顺序一致，说明活化能与指前因子有相互的补偿效应，并且甘油水重整制氢有最佳的颗粒度。红外谱进一步证明Ni颗粒度的变化，没有影响表面活性物种的种类，即没有影响反应机理。催化剂LaNi-Al2O3和CeNi-Al2O3上甘油/水脉冲反应在475 ℃到525 ℃反应温度范围内，CeNi-Al2O3上甘油/水脉冲反应具有高的氢转换频率。水的氢转换频率在各个催化剂上相当，说明La2O3和CeO2并没有影响水的解离生成氢。二次脉冲甘油/水的氢转化频率均低于初次脉冲结果，表明反应稳定前催化剂有一个钝化过程。助剂La2O3和CeO2的加入，降低了反应积碳量。La2O3助剂较CeO2助剂更有助于降低反应的积碳量。通过动力学分析，在LaCeNi-Al2O3催化剂上具有较低的消碳活化能。说明在LaCeNi-Al2O3催化剂上的解离的碳物种是比较容易反应的。