同步合成之含鉻金屬有機框架(Cr-MOF-199)及其孔洞衍生氧化銅/亞鉻酸銅複合物應用於提升酚羥化反應

Abstract

本研究目的是應用原位合成法(De novo synthesis)合成具孔洞之氧化銅/亞鉻酸銅複合物(CuCr2O4/CuO)應用於提升酚羥化 (hydroxylation)反應之選擇性。為了設計雙金屬固體催化劑，含銅之金屬有機框架(MOF-199)被選為裝載活性物質鉻之載體，並經由原位合成法同時組合鉻及載體。此鉻嵌入之金屬有機框架(Cr-MOF-199)被進一步燒成氧化銅/亞鉻酸銅複合物。此樣品並經由X光繞射(XRD)、掃描式電子顯微鏡(SEM)、穿隧式電子顯微鏡(TEM)及氮氣吸脫附進行分析。結果顯示，我們成功將鉻離子均勻嵌入金屬有機框架之中，其構型並隨著鉻含量的增加由八面體轉變為立方體。此具有孔洞之氧化銅/亞鉻酸銅複合物被進一步應用於酚羥化反應，並在最佳條件下有40%之二酚(diphenols)產率(包含鄰苯二酚及對苯二酚)。值得一提的是，由於亞鉻酸銅的存在，鄰苯二酚(catechol)及對苯二酚(hdroquinone)之間的選擇性(catechol/hydroquinone)由1.3增加至1.8。此應用氧化銅/亞鉻酸銅複合物提升酚羥化反應選擇性提供了金屬有機框架衍生觸媒(MOF-derived catalysts)全新的應用。

The purpose of this study is to synthesize porous copper chromite/copper oxide (CuCr2O4/CuO) composites by a de novo synthesis of Cr-doped metal organic framework (MOF) as effective catalysts for phenol hydroxylation with enhanced selectivity. To desgin and synthesize a bimetallic solid catalyst, MOF-199 with copper source was chosen as the support for incorporating active species (i.e. Cr) through a de novo synthesis route, i.e. chromium ions were encapsulated into MOF-199 simultaneously upon the formation of the MOF-199 framework. The obtained Cr-MOF-199 samples were further calcined to convert into CuCr2O4/CuO composites that were characterized with XRD, SEM, TEM, and nitrogen sorption. The results showed that chromium ions were successfully embedded in the structure of MOF-199 uniformly, and the morphology of Cr-MOF-199 was changed from octahedral to cubic when chromium content was increased. The obtained porous CuCr2O4/CuO composites were further applied in phenol hydroxylation, and the results showed a high yield of 40% for diphenols (including hydroquinone and catechol) in optimized reaction conditions. It is worth of noting that the ratio of catechol/hydroquinone was enhanced from 1.3 to 1.8 with the existence of our synthesized CuCr2O4/CuO composites. The enhanced selectivity of catechol in phenol hydroxylation catalyzed by our newly synthesized CuCr2O4/CuO composites would provide a new application of MOF-derived catalysts.