原子尺度分散的钯催化剂上丁二酸加氢反应机制

Considering the consumption and the limited nature of the fossil fuels, great efforts are being investigated to develop a chemical industry based on renewable resources as substitute for the dwindling fossil fuels using green chemistry manufacture. Succinic acid is one of the most important bio-derived building-block chemicals. The main scientific and technological issue is to improve the active efficiency of nanoscaled palladium (Pd) catalysts and the selectivity of γ-butyrolactone (GBL) for succinic acid hydrogenation. Supported nanoscaled Pd catalysts have been demonstrated very promising activity and selectivity in many industrial processes. The catalytic properties of heterogeneous Pd catalysts have been found to strongly depend on the particle size and stability. However, the Pd nanoparticles are mobile on the surface of most supporting oxides and aggregated under reaction conditions, which not only reduces the atom efficiency but also leads to undesired side reaction. Some appropriate oxides that strongly interacting with the Pd species can prevent this aggregation. Moreover, they can create stable, finely dispersed Pd species or clusters with high catalytic activity and selectivity. The ultimate small sized Pd particles are atomically dispersed catalysts and have attracted a great deal of attention from experimental and theoretical studies. This proposal aims to design and prepare a series of atomically dispersed Pd catalysts based on facile wet chemistry. The forming mechanism, structure and properties of these synthesized catalysts would be characterized and explored by high angle annular dark field scanning transmission electron microscope (HAADF-STEM), TEM, SEM, X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure spectroscopy (EXAFS), and so on. The catalytic activity and stability for succinic acid hydrogenation to GBL will be analyzed based on theory and experimental. The hydrogenated mechanism would be considered by reacted kinetic model, in situ Fourier Transform Infrared spectroscopy (FT-IR) and physical chemistry properties. Based on this project, a facile wet chemical approach for synthesis of atomically dispersed Pd catalysts will be proposed, and bio-derived succinic acid hydrogenation will be provided by these catalysts, which are hopefully expected to applicable for the integration of chemical catalysis and biological fermentation.

利用化学反应过程将可再生资源生物基平台化合物- - 丁二酸转化为高附加值化学品，是资源、生工和化工领域的重要研究方向。本项目针对提高平台化合物丁二酸加氢反应过程中钯催化剂的原子利用效率和选择性的核心问题，提出采用简单的湿化学方法来设计并合成不同结构的原子尺度分散的钯催化剂；利用密度泛函理论计算其表面自由能；通过现代表征技术研究原子尺度Pd催化剂的结构、性质，以及载体和Pd物种之间的相互作用；研究原子尺度Pd催化剂上丁二酸加氢合成γ-丁内酯反应性能，建立反应动力学模型，并利用原位波谱技术结合物化表征推测加氢反应机理。本项目不仅可以获得具有自主知识产权的原子尺度分散的Pd催化剂，为合成高活性、高选择性和高稳定性催化剂提供理论和实验依据，而且可以实现生物基平台化合物的催化转化，具有重要的基础研究意义和应用参考价值。

将可再生资源生物基平台化合物—丁二酸转化为高附加值化学品，是资源、生工和化工领域的重要研究方向。针对平台化合物丁二酸加氢反应过程中钯催化剂的原子利用效率和选择性低的核心问题，我们采用简单的湿化学方法设计并合成4种原子尺度分散的钯催化剂。他们分别是氨基功能化核壳型SiO2微球负载钯催化剂（Pd/SiO2-NH2）、TiO2纳米片负载钯催化剂（Pd/TiO2），氧化铝和氧化锆负载原子尺度分散的钯催化剂（Pd/γ-AlOOH，Pd/ZrO2）。这些高效的原子尺度分散的钯催化剂为丁二酸加氢还原工业化提供技术参考。.我们利用现代表征技术对制备的催化剂进行了结构、组成、Pd分散度及粒径分布等方面的分析。Pd/SiO2-NH2利用N-氨乙基-γ-氨丙基三甲氧基硅烷有效提高钯粒子在载体上的分散度。1.0% Pd/SiO2-NH2在以1,4-二氧六环作溶剂，在240°C，60 bar H2下反应4 h，丁二酸转化率为100%，γ-丁内酯选择性达94%。0.2 Pd/γ-AlOOH可实现丁二酸63%的转化率和γ-丁内酯95%以上的选择性；结果表明单原子分散的Pd1反应活性为305.4 h-1，是相同条件下Pd13团簇中每个原子活性的30倍，是Pd55团簇中每个原子活性的1100倍。因此原子尺度分散钯催化剂是丁二酸选择性加氢还原的高效催化剂，具有很高的研究价值。.为提高原子尺度分散钯催化剂的水相稳定性和循环利用效率，我们制备了Pd/TiO2和Pd/ZrO2催化剂。1.0% Pd/TiO2 (400)在200°C，100 bar H2下反应8 h，丁二酸转化率为90%，γ-丁内酯选择性达94%。微波水热法合成的0.2Pd/ZrO2，丁二酸转化率为63%，γ-丁内酯选择性为95%。这两种催化剂在水溶液中、酸性环境下高效催化丁二酸加氢，且保持良好的稳定性。这些高活性、高稳定性、价格低廉、制备便捷的优点，降低了丁二酸加氢还原反应和分离成本，为工业化提供可能。此外，利用DFT理论计算钯原子团簇在载体表面的吸附过程，以及氢在催化剂活性位上的分子吸附和解离过程。结果表明氢分子在单原子钯上易发生吸附，解离吸附又较稳定，所以单原子钯容易催化氢气吸附—H-H键断裂这一过程，对加氢还原反应具有高活性。