介孔氧化钛表面反应与传递调控机制的介尺度分子模拟

Mesoporous materials show great prospect in heterogeneous catalysis. However, the reaction and transportt in mesopores differ from that in the macro-scale, so the complicated structure and intra/interaction of the interface must be clarified to reveal the mechanism of regulation. The activity of catalyst could be improved by mesoporous TiO2. But various crystal facets make the recognizing of surface property difficult. The experimental phenomena are due to both complex structures and interactions in varied scales. It is necessary to care about not only catalysis mechanism but transport for the design of catalyst with nano/micro mesopore structures. The microscopic phenomena can not be accurately analyzed by only using simple experiment. Using molecular simulation it has been found that the flow of polar liquid on the surface of TiO2 can be improved significantly. Quantum calculation show that water molecules can dissociate on activited TiO2 crystal surfaces. It makes TiO2 crystal surfaces acted different Brønsted acid-base properties and then affects their catalytic properties. Coupling different simulation methods is needed to consider the behavior of fluid on rough interface with reaction. We can investigate the reaction mechanism and the relationship between changes of the composition quantitatively, using Reax-ff method which considering reaction and transition simultaneously for a large system. Due to a greater impact of interfacial roughness on the stability of the catalytic, the new method “interface coarse-grained mesoscopic simulation” should be adopted. The wall sliding non-equilibrium MD simulation is introduced to study the viscosity, friction coefficient, etc. to set up mass transfer model in mesoscopic scale for transition of heterogeneous catalysis.

介孔材料在多相催化中表现良好应用前景。但介质在介孔内的反应和传递不同于宏观，必须弄清界面复杂结构和作用，才能揭示其调控机制。介孔TiO2可显著提高催化剂活性，但由于多种晶型晶面存在，人们对其表面认识不清。实验现象是不同尺度复杂结构和作用力共同作用的结果，对于具有纳微介尺度孔道催化剂的设计，其传递和催化反应机制须同时关注。单纯实验表征无法精确分析微观现象；分子模拟发现TiO2表面极性流体流动显著提高。量化计算发现水分子在高活性TiO2晶面自发解离，表现不同的Brønsted酸碱性，影响其催化性能。对于带反应的粗糙界面处流体的行为，需要耦合现有模拟方法。反应力场方法同时考虑反应和传递，且能针对较大体系，可定量考察反应机理及体系组成变化的关系。界面粗糙度对催化稳定性影响很大，须采用界面粗粒化的新介尺度模拟方法处理。壁面滑动非平衡MD用来考察体系粘度、摩擦系数等性质，建立介尺度下多相催化传质模型。

介孔材料在多相催化中表现良好应用前景。但介质在介孔内的反应和传递不同于宏观，必须弄清界面复杂结构和作用，才能揭示其调控机制。介孔TiO2可显著提高催化剂活性，但由于多种晶型晶面存在，人们对其表面认识不清。本项目合成了TiO2担载的催化剂，并将催化剂用于直接法合成H2O2反应体系和CO2催化加氢转化，H2O2在载体表面的吸脱附性质与最终产物选择性存在密切关系，在Pd-TiO2(B)/anatase催化剂表面H2O2的选择性提高了57%。通过分子模拟发现在TiO2(B)/anatase复合载体表面H2O2的脱附比在anatase载体表面容易得多，从而揭示了催化剂介尺度结构的性能调控机制。实验现象是不同尺度复杂结构和作用力共同作用的结果，对于具有纳微介尺度孔道催化剂的设计，其传递和催化反应机制须同时关注。本项目研究了离子液体膜厚对离子液体捕集CO2的影响以及负载离子液体吸收和解吸CO2机制，首次解释了CO2传质速率大幅提高的前提是离子液体膜厚在纳米尺度。通过气体吸收解吸实验以及基于非平衡热力学的动力学分析，建立了溶解-扩散模型，发现载体表面离子液体的膜厚是影响气-液传质的关键和可调控因素。单纯实验表征无法精确分析微观现象；分子模拟发现TiO2表面极性流体流动显著提高。对于带反应的粗糙界面处流体的行为，需要耦合现有模拟方法。界面粗糙度对催化稳定性影响很大，须采用界面粗粒化的新介尺度模拟方法处理。项目分别通过AFM测试和粗粒化模拟对蛋白及大分子团簇的界面吸附和界面相行为进行了研究，发现介孔TiO2界面几何粗糙度对于蛋白吸附性能的影响，为进一步建立基于TiO2的粗粒化力场提供基础。本项目的研究内容为初步建立介尺度下多相催化传质模型奠定了基础。