偶联剂辅助的“NPs@Oxides”类核-壳结构跨尺度自组装及其甲烷干气重整性能研究

The ‘core-shell’ nanostructure is a promising protocol to inhibit the sintering of nanoparticles and enhance the catalyst stability, but its effective and efficient catalyst engineering remains significantly challenging. Herein, with the aid of well-defined cross-linking molecules, we propose a chemically and economically affordable strategy to catalytically functionalize the monolithic ‘Foam/Fiber’ substrates by the ‘core-shell’ nanostructure. Concretely, the different building blocks (such as Ni nanoparticles, SiO2 shell and Foam/Fiber substrate) can be precisely organized into the monolithic structured ‘core-shell’ catalyst in one step with the aid of APTES (one kind of cross-linking molecules) via properly controlling reactions (i.e., the chelation between Ni2+ and -NH2 in APTES, and the silanisation between -Si-O-CH2-CH3 and Foam/Fiber). Such monolithic structured ‘core-shell’ catalyst is able to collaboratively couple “the catalytic performance of ‘core-shell’ nanostructure and the reaction process intensification”. Effects of the kinds of cross-linking molecules, transition metal precursors, and Foam/Fiber chemical modifications, etc., will be systematically investigated on the one-step organization of this catalyst from nano- to macro-scales. And the one-step organization principle of ‘chelation, interface reaction coupling, and organization of ‘core-shell’ nanostructure via controllable hydrolysis reaction’ will be illustrated. In particular, the organization of the monolithic Foam/Fiber structured ‘Ni@Oxides’ catalysts with the aid of cross-linking molecules and their application in the dry reforming of methane are to be explored. The effects of Ni particles size and shape, the porous structure and composition of oxides-shell, and substrate structure and properties will be systematically studied on the sintering/coking resistance and heat/mass transfer property.

‘核-壳’纳米结构催化剂工程化是当前纳米催化领域极富挑战性的课题。提出了‘偶联剂’辅助的整装Foam/Fiber基体‘核-壳’纳米结构催化功能化新策略，即利用偶联剂的双向（配位络合和缩合偶联）化学键合作用，将不同的结构单元（如Ni纳米颗粒、SiO2壳层和Foam/Fiber基体）一步自组装而成整装‘核-壳’纳米结构催化剂，实现“核-壳结构催化特性-反应过程强化”的协同耦合。研究偶联剂结构与组成、过渡金属盐前体、Foam/Fiber骨架化学改性对‘核-壳’纳米结构一步跨尺度自组装的影响，阐明‘配位络合-界面化学反应偶联-核壳结构可控组装’多步协同匹配规律。侧重开展抗积炭、抗烧结、高导热甲烷干气重整Ni@Oxides/Foam(Fiber)整装催化剂的偶联剂辅助构筑，阐明Ni纳米颗粒尺寸和形态、Oxides壳孔结构和化学组成等物化特性以及基体结构与材质特性对抗烧结、抗积碳和热质传递的影响关系。

甲烷重整和部分氧化制合成气是天然气间接转化利用的核心课题之一，抗积碳、抗烧结和强化传热Ni基催化剂的研制是难点和关键。以具有强化传质/传热、高渗透性的孔结构工程化的整装金属材料为载体，通过化学刻蚀、界面辅助生长及偶联剂辅助一步自组装等表/界面催化功能化的整装结构催化剂制备新策略和新技术，研制了一系列金属Foam/Fiber结构化Ni基催化剂，实现了反应器内流动和传递与表界面催化反应的协同耦合，该类催化剂表现出良好的甲烷部分氧化(POM)及甲烷干重整(DRM)制合成气催化性能。采用化学刻蚀、原位生长、溶胶辅助浸渍等策略，制备了一系列用于POM反应的Ni-foam和FeCrAl-fiber结构化Ni催化剂。主要结果有：（1）化学刻蚀法所制NiO-Al2O3/Ni-foam具有高活性和选择性，但易积炭；以水热法和溶胶辅助浸渍法分别制得的Foam/Fiber结构化水滑石（LDHs）衍生NiO-MgO-Al2O3和Ni-CeAlO3-Al2O3催化剂，具有高活性和选择性且稳定性良好。（2）LDHs衍生NiO-MgO-Al2O3催化剂中各组分高度分散、Ni物种与助剂的相互作用强并具有一定碱性，提高了Ni纳米颗粒的抗烧结和抗积炭能力； Ni-CeAlO3-Al2O3催化剂中Ce3+/Ce4+氧化还原循环利于Ni纳米颗粒上积碳物种的转化消除。（3）以AlOOH修饰的FeCrAl-Fiber为载体，借助3-氨丙基三乙氧基硅烷（APTES）的双向桥联作用，实现了Ni2+、APTES和AlOOH的一步自组装，经热处理获得微纤结构化类核壳Ni@SiO2/Al2O3/FeCrAl-fiber催化剂；基于SiO2壳层的限阈效应、Ni-SiO2之间的强相互作用及FeCrAl-fiber良好的传质/传热性能，该催化剂对DRM反应具有高活性、高抗积碳和良好的抗烧结性能，在800 oC下稳定运行500 h无失活迹象且无积碳生成；反应后Ni@SiO2类核壳结构保存完好，Ni颗粒尺寸仅从还原后的7-9 nm增大到10-16 nm，且未检测到积炭的生成。