A Spectroscopic Study of Supported‐Phosphate‐Catalysts (SPCs): Evidence of Surface‐mediated Hydrogen‐Transfer
A Spectroscopic Study of Supported‐Phosphate‐Catalysts (SPCs): Evidence of Surface‐mediated Hydrogen‐Transfer
复制标题
负载型磷酸盐催化剂 (SPC) 的光谱研究：表面介导的氢转移的证据
DOI：
10.1002/cctc.202001897
复制
发表时间：
2021
期刊：
影响因子：
4.5
通讯作者：
Baltrusaitis, Jonas
中科院分区：
文献类型：
--
作者：
Kiani, Daniyal;Baltrusaitis, Jonas
负载型磷酸盐催化剂（SPCs）是一种用途广泛的非均相材料，用于各种工业相关工艺，包括Fischer - Tropsch合成（FTS）、nox与NH3的选择性催化还原（SCR）和C2H5OH到n - C4H9OH的Guerbet反应。本文采用原位化学探针温度-程序升温-解吸红外光谱技术，研究了用磷酸浸渍不同载体合成的SPCs模型。在所有SPCs的温度上升过程中，都观察到催化剂表面的羟基化。在相同的实验中，在裸支撑上没有观察到这种行为。结果表明，表面羟基化反应是通过牺牲氢转移反应发生的，其中化学探针（nh3或C2H5OH）可以用作氢供体。结果还表明，氢转移反应的程度和速率取决于载体、磷酸盐负载和氢供体分子的特性。表面Brønsted酸位点（P−OH）不参与反应，P=O表面位点被认为是观察到的氢转移的活性位点。基于目前的工作，我们建议任何涉及磷酸盐促进或磷酸盐基催化剂加氢的催化反应都需要考虑在整个反应机制中磷酸盐位点的表面介导的氢转移能力。
Supported‐phosphate‐catalysts (SPCs) are a versatile class of heterogeneous materials used in various industrially relevant processes including Fischer‐Tropsch synthesis (FTS), selective catalytic reduction (SCR) of NOxwith NH3, and Guerbet reaction of C2H5OH to n‐C4H9OH. Herein, model SPCs synthesized by impregnating various supports with phosphoric acid were studied usingin‐situchemical probe temperature‐programmed‐desorption infrared spectroscopy. Hydroxylation of the catalyst surface was observed during the temperature ramp on all SPCs. This behavior was not observed on the bare supports during identical experiments. The results indicate that hydroxylation of the surface occurs via sacrificial hydrogen‐transfer reaction, where the chemical probe (NH3or C2H5OH) can be utilized as the hydrogen‐donor. Results herein also show that the extent and the rate of hydrogen‐transfer reaction depend on the identity of the support, phosphate loading, and identity of the hydrogen‐donor molecule. Surface Brønsted acid sites (P−OH) do not contribute to the reaction and P=O surface sites are proposed as the active sites for the observed hydrogen‐transfer. Based on the current work, it is suggested that any catalytic reaction that involves hydrogenation over phosphate‐promoted or phosphate‐based catalysts needs to account for the surface‐mediated hydrogen‐transfer capability of the phosphate sites in the overall reaction mechanism.