Rh/SiO_2和Rh/NaY催化剂上合成气反应的高压原位红外光谱研究  

In-situ FT-IR Study of High Pressure Syngas Conversion over Rh/SiO_2 and Rh/NaY Catalysts

作　　者：孙科强[1] 徐柏庆[1] 朱起明[1] 翁维正[2] 万惠霖[2] 

机构地区：[1]清华大学化学系,一碳化工国家重点实验室,北京100084 [2]厦门大学固体表面物理化学国家重点实验室,厦门361005

出　　处：《化学学报》2001年第1期22-27,共6页Acta Chimica Sinica

基　　金：国家自然科学基金 ( 2 98430 0 4);清华大学基础研究基金(JC19990 5 1);厦门大学固体表面物理化学国家重点实验室开放基金资助项目

摘　　要：采用高压原位FT -IR技术 ,对比研究了CO加H2 反应条件下Rh/SiO2 和Rh/NaY催化剂表面反应中间物种 .在Rh/SiO2 表面上 ,无论在常压还是在 1.0MPa合成气中 ,只观察到线式和桥式吸附CO .而在常压合成气中 ,Rh/NaY上不仅存在上述CO吸附物种 ,而且还有孪生型的Rh(I) (CO) 2 和少量Rh6 (CO) 16 ;当合成气压力升至 1.0MPa后 ,Rh(I) (CO) 2 迅速转化成Rh6 (CO) 16 和在 2 0 42cm-1产生吸收的单核羰基Rh物种 ,与此同时催化剂表面还生成了单齿和双齿乙酸根物种 ;这些在高压下生成的物种在合成气压力重新降回到常压时依然稳定存在 .研究Rh/NaY上合成气反应表面物种与H2 的反应行为表明单齿乙酸根很可能是反应的活性中间物 .High pressure syngas [V(CO) : V(H-2) = 1] conversion over unpromoted Rh catalyst supported on silica and zeolite NaY were studied at 250 degreesC with an in-situ. IR cell that avoided contamination of iron carbonyls. Change of the syngas pressure produced no effect on the IR spectrum of Rh/SiO2; bridged and linear CO on Rh clusters were the only detectable surface species under 0.1 to 1.0 MPa of flowing syngas. In addition to the bridged and linear CO species, two types of dicarbonyls [Rh(I)(CO)(2)] and a small amount of Rh-6(CO)(16) were formed when Rh/NaY was exposed to 0.1 MPa syngas. Increasing of the syngas pressure to 1. 0 MPa over Rh/NaY resulted in transformation of the dicarbonyls to Rh-6(CO)(16) and probably a mononuclear medium carbonyl featuring an absorption 2042 cm(-1). The detectable reaction products adsorbed on Rh/NaY catalyst under 1.0 MPa were monodentate and bidentate acetates. These surface species were maintained even after releasing the syngas pressure back to 0.1 MPa. Thus, a remarkable difference exists in the effect of syngas pressure on the strtucture of Rh catalysts: reconstruction of Rh catalyst under high pressure of syngas occurs in zeolite NaY but not on silica. Reactivity of the adsorbed surface species toward hydrogen after the catalyst reconstruction suggests that the monodentate acetate groups are responsible for the selective formation of acetic acid from syngas over the Rh/NaY catalyst.

关 键 词：催化剂重构 羰基铑物种 合成气 原位红外光谱 乙酸 选择性反应 负载型铑催化剂 二氧化硅 钇化钠 

分 类 号：O643.3[理学—物理化学]