耐酸性磷化钼结构对氢氟氯烃加氢脱氯反应性能调控机制

Hydrodechlorination (HDC) is an effective strategy for the synthesis of environmentally hydrofluoroolefins (HFOs). However, the high temperature and strong acidic reaction conditions make the non-noble metal catalysts still have problems such as low reactivity and easy deactivation. This has become a bottleneck problem in the promotion and application of HDC in preparing of HFOs. The excellent reactivity and acidic condition stability of the sulfur-containing phosphide catalysts bring a glimmer of hope to the breakthrough of this process, but the direct preparation of sulfur-containing phosphides under mild conditions remains a challenging issue. According to the fact that the P-S bond is weaker than the P-O, this project proposes a new strategy of forming molybdenum phosphide (MoP) with a sulfur-containing active phase by replacing the metal phosphate with a non-oxygen phosphosulfide salt. Consequently, reveal the factors affecting the catalyst phase and bonding structure and its mechanism. The activity and product distribution of HDC of 1,1,1,2-tetrafluoro-2-chloropropane (HCFC-244bb) will be investigated over sulfur-containing MoP catalysts. The reaction results will be quantitatively correlated with the composition and structure of the sulfur-containing active phase, which are characterized by N2 adsorption-desorption, CO-chemisorption, XRD, TEM, SEM, XPS and XRF. The intrinsic relationship between the composition and structure of sulfur-containing active phase and its acid resistance and high reactivity of HDC will be determined. Based on the research of this project, the preparation method of high activity and acid-resistant hydrodechlorination phosphide catalyst was established, which provided theoretical and experimental basis for the process of hydrodechlorination synthesis of HFOs.

加氢脱氯是合成环境友好型氢氟烯烃的有效策略。由于反应所需高温及强酸性条件，目前非贵金属催化剂存在反应活性低且易失活等问题，限制了加氢脱氯合成氢氟烯烃工艺的推广应用。含硫磷化物催化剂优异的反应活性和酸性条件稳定性给这一工艺的突破带来一线希望，但温和条件下直接制备含硫磷化物仍是一个挑战性课题。本项目依据P-S键弱于P-O键的事实，提出以不含氧磷硫盐取代金属磷酸盐在低温下形成具有含硫活性相的磷化钼新策略。围绕该策略，探索影响催化剂物相及键合结构特征的关键因素；以催化2-氯-1,1,1,2-四氟丙烷气相加氢脱氯为模型反应，揭示催化剂活性和产物分布规律；通过对反应前后不同物相及结构特征含硫磷化钼催化剂的表征，并与反应结果关联，阐明含硫磷化钼催化氢氟氯烃加氢脱氯的活性及耐酸性机制。基于本项目研究，建立高活性及耐酸性加氢脱氯磷化物催化剂制备方法，为加氢脱氯合成氢氟烯烃工艺推广提供理论与实验基础。

加氢脱氯（HDC）是合成环境友好型氢氟烯烃的有效策略。由于反应所需高温及强酸性条件，目前非贵金属催化剂存在反应活性低且易失活等问题，限制了加氢脱氯合成氢氟烯烃工艺的推广应用。富金属过渡金属磷化物表现出金属的特性，在加氢精制等诸多反应中显示出良好的性能。但是应用于选择加氢脱氯合成氢氟烯烃反应中仍存在催化剂制备条件苛刻和样品在高温酸性反应环境下的结构稳定性差等问题。本项目利用P-S键键能比P-O键弱这一特性，提出以不含氧的磷硫盐（(NH4)4P2S6）与钼酸铵的混合物替代磷酸盐作为前驱体制备含硫MoP催化剂的新方法，研究了催化剂物相及键合结构特征的关键因素及新方法制备的含磷硫化物催化2-氯-1,1,1,2-四氟丙烷气相加氢脱氯合成2,3,3,3-四氟丙烯的反应性能。结果表明，以(NH4)4P2S6与钼酸铵的混合物为前驱体在较低的H2压力（0.1MPa），450oC温和条件下成功制备出MoP催化剂（MoP-S）。制备过程中前驱体中的硫掺杂到MoP晶相中，整个MoP-S催化剂就是一个含硫相。MoP-S催化剂在HDC反应中表现出优异的反应活性和稳定性，但是由于加氢性能太强，目标烯烃产物的选择性不高。因此，通过第二金属组分添加对MoP-S进行改性拓展探究。通过对几种不同金属（钾、铜和银）的筛选，得到较高目标产物选择性的CuMoP-S催化剂，相同反应条件下，目标产物的选择性达到80%。通过本项目的实施，建立了采用硫代磷酸盐低温直接合成含硫磷化物的新方法，揭示了含硫磷化物催化剂的结构特征对其活性及耐酸性的影响机制，发展了磷化物应用于氢氟烃加氢脱氯的新工艺，对目前针对氢氟烯烃化学品的绿色低碳合成有一定的借鉴意义。