二碘烷化合物在銅(111)單晶表面吸附與反應研究

Adsorption and Reactions of Diiodoalkanes on the Cu(111) Surface

10.6623/chem.2002045

楊日豪(Jih-Hao Yang)；蔣昭明(Chao-Ming Chiang)

表面化學 ； 次甲基 ； 程序控溫反應/脫附 ； 反射吸收紅外光譜 ； Surface chemistry ； methylene ； temperature-programmed reaction/desorption ； reflection absorption infrared spectroscopy

化學

60卷3期（2002 / 09 / 01）

463 - 482

繁體中文

次甲基(:CH_2)是Fischer-Tropsch合成法製造各種直鏈烷類的一個重要中間體。本研究企圖以CH_2I_2為前驅物吸附在銅(111)表面上產生次甲基，藉由程溫反應/脫附與反射式吸收紅外光譜實驗觀察次甲基於表面上的鍵結及反應。配合CD_2I_2的實驗可知在不同吸附量的條件下，會產生前驅態及化學吸附態的次甲基，而這些次甲基在不同溫度行自身偶合反應生成乙烯脫附。而在分子多層吸附情況則可觀察到CH_2I_2的相變化，在142K以下為phase I'在172K以上則為phase II。至於1,3-二碘丙烷在低溫鋼( 111 )上也可同時斷兩碳-碘鍵生成三碳金屬環化物中間體，隨表面溫度升高部分金屬環化物關環生成環丙烷於160K脫附，其餘三碳金屬環化物則會消去β-H生成n^3-allyl中間體，再y轉化成表面n^1-propenyl物種，最終與表面上的氫原子反應生成丙烯於215K脫附。至於其多層分子薄膜則可觀察到兩種構形的變化，160K以下為GG構形，190K以上則轉化為AA構形。

The adsorption of diiodomethane and 1,3-diiodopropane on Cu(111) was studied by temperature programmed reaction/desorption(TPR/D) and reflection-absorption infrared spectroscopy(RAIRS). CH_2I_2 adsorbs dissociatively at low coverages and molecularly at high coverages. The dissociative adsorption yields ＂hot precursor＂ state and chemisorbed state methylenes on the surface. The formation of C_2H_4 via the precursor state occurs at 145K, and via chemisorption state takes place at 175K. At high coverages, molecular CH_2I_2 escapes into the gas-phase at 195K, followed immediately by C_2H_4 desorption. For CH_2I_2 multilayers, a metastable phaseI' exists below 142K and a phase transition to phaseII occurs at 172K. Adsorbed 1,3-diiodoproane (DIP) decomposes to a C_3 metallacyclic intermediate at 120K. A portion of the metallacycles undergoes a ring closure reaction to form cyclopropane at 160K. The rest dehydrogenates via a β-hydride elimination step to form allylic moieties on the surface. The allylic species hydrogenate to propene and finally desorb at 215K. For multilayer DIP, phase transition is also observed by RAIRS. At low temperatures, the GG conformation is clearly more favorable, but at near 190K the GG is transformed into the AA conformation.