利用近室壓X光光電子能譜探究鋅鈀和鋅鈀銅奈米顆粒催化二氧化碳氫化反應

Ambient Pressure X-ray Photoelectron Spectroscopy study of carbon dioxide hydrogenation on PdZn and PdCuZn (3:1:4) nanoparticles

將二氧化碳透過適當的催化劑轉換成可用的化學物質以減少地球上二氧化碳的含量是當前研究重要的課題之一。近年來鋅鈀與鋅鈀銅奈米顆粒已被報導具有潛力於常壓下將二氧化碳氫化成可用的化學分子。本篇將報導利用微濕含浸化學合成法合成鋅鈀與鋅鈀銅奈米顆粒，透過X光粉末繞射儀、穿透式電子顯微鏡、氣相層析儀了解所合成出的奈米顆粒大小、結晶相與催化特性，並利用近室壓X光光電子能譜臨場探究鋅鈀與鋅鈀銅奈米顆粒進行二氧化碳氫化反應過程中催化劑表面狀態的改變及產物的生成過程。由實驗結果得知，鋅鈀與鋅鈀銅奈米顆粒大小分別為10- 15奈米及10- 25奈米且可以催化二氧化碳氫化生成不同比例的一氧化碳、甲烷及乙烷，其中鋅鈀銅奈米顆粒相對於鋅鈀奈米顆粒產生較少的一氧化碳及較多量的甲烷、乙烷，由臨場近室壓X光光電子能譜中發現鋅鈀奈米顆粒於反應中除了有鋅鈀合金之外亦有金屬鈀的成分存在，推測由表面金屬鈀所形成的氧化鈀是為鋅鈀奈米顆粒相較於鋅鈀銅奈米顆粒產生較多一氧化碳，而在鋅鈀銅奈米顆粒表面則可以透過生成甲酸基做為產生烷類前驅物因此可以產生較多的甲烷與乙烷產物。

Converting carbon dioxide into low chemical molecules to reduce the amount of CO_2 in the earth is one of the emerging research topics recently. PdZn and PdCuZn nanoparticles have been reported as potential catalysts for CO_2 hydrogenation under ambient pressure. In this report, the PdZn and PdCuZn (3:1:4) nanoparticles were prepared by using the impregnation method, and the particles size、crystallinity, and catalytic property were characterized by X-ray diffraction patterns (XRD)、transmission electron microscopy (TEM), and gas chromatography (GC), respectively. In addition, the surface chemical environment evolution of PdZn and PdCuZn (3:1:4) nanoparticles and the formation of the products during the carbon dioxide hydrogenation were studied by using ambient pressure X-ray photoelectron spectroscopy (APXPS). According to experimental results, the PdZn and PdCuZn (3:1:4) particle sizes are 10-15 nm and 10- 25 nm, respectively, and have a higher carbon monoxide production rate on PdZn nanoparticles compared to PdCuZn (3:1:4) nanoparticles. The Pd 3d spectra showed the PdO and PdZn on the PdZn nanoparticles, and the most formate was observed on the PdCuZn (3:1:4) nanoparticles from Cls spectra during the carbon dioxide hydrogenation from in-situ APXPS studies. We proposed that the metallic Pd was oxidized to be PdO on the surface of the PdZn nanoparticles, and the formation of methane via formate pathway could be the significant reason for different production ratios on PdZn and PdCuZn (3:1:4) nanoparticles.