製備多孔性磷酸化TixZr1-xO2之固態酸吸附材與其特性鑑定

Abstract

本研究以離子液體輔助水熱法合成多孔性磷酸化TixZr1-xO2固態酸吸附材，並利用N2吸脫附, XRD, TEM, ESCA, ICP-MS, pyridine-FTIR 以及NH3-TPD進行材料微結構，化學組成與表面酸性的鑑定。結果顯示0.4P-Ti0.5Zr0.5O2樣品具有最高的比表面積278 m2/g，元素的莫耳比P/Ti/Zr = 2：1：1，磷酸為表面酸性的主要來源，此外Ti4+與Zr4+離子不同的氧配位數也為材料帶來額外的酸性位置，樣品表面酸性型態以Bronsted acid為主，P5+的高電負度分別在表面創造以P-OH與Ti-OH/Zr-OH為主的弱與中弱酸Bronsted acid，總酸性位置數量可高達1.27 mmol/g。由於Ti4+、Zr4+、與P5+在結構當中能在高溫鍛燒的情況下互相抑制彼此晶相的形成，材料在650 C以下仍可維持高比表面積，NH3氣重複吸脫附的結果顯示材料由於脫水反應，NH3脫附量僅在第一次循環後降低10%，在後續的循環過程中即維持穩定，顯示材料未來在應用上的高重複使用性。

In this study, phosphated TixZr1-xO2 solid acids with porous structures were prepared by using an ionic-liquid-assisted hydrothermal method. The microstructures, chemical compositions, and surface acidity of resulting materials were characterized by N2 adsorption/desorption, XRD, TEM, ESCA, ICP-MS, pyridine-FTIR and NH3-TPD. The 0.4P-Ti0.5Zr0.5O2 powders, in which the P/Ti/Zr = 2：1：1, exhibited the highest surface area of 278 m2/g. Phosphate species dominates surface acidity. In addition, the different oxygen coordinations between the Ti4+ and the Zr4+ ions bring extra surface acid sites. Brönsted acids are the primary type of the acids. High elecronagativity of the P5+ ions leads to weak and medium Brönsted acidity on the P-OH and Ti-OH/Zr-OH sites, respectively. The total amount of acidic sites is 1.27 mmol/g. There are little amounts of Lewis acid sites on the surface until 650 C. The Ti4+, Zr4+ and P5+ ions in the matrix inhibit the grain growth during thermal treatment and maintain the high surface areas. The sample exhibited high thermal stability during repeated NH3 adsorption and desorption cycles. The quantity of the desorbed NH3 molecule declined only by 10% due to dehydroxylation after the first cycle and maintained constant in the following cycles, indicating the high reusability of the material in the applications.