Selenium-doped hexarhodium carbonyl clusters on magnesia: structures and promoting effects in ethene hydroformylation

Abstract

Selenium-modified Rh6(CO) 16/Mg0 catalysts were prepared by the reaction of Rh6(CO)16/Mg0 with (CH3)2Se in order to examine the promoting effect of an electronegative additive on Rh catalysis for ethene hydroformylation. The deposited Se (Se/Rh6 = 0.6) enhanced the rate of propanal formation 1.9 times as compared with the case of an undepited catalyst.The selectivity of the hydroformylation was improved from 20 to 50% by the Se addition. To the contrary, the monotonous suppression of ethane formation by increasing the Se amount was observed. Further doping of Se reduced the hydroformylation activity. TPD, IR, and Se K-edge and Rh K-edge EXAFS revealed that (CH3)2Se reacted with the Rh atoms of partially-decarbonylated Rh, species on the MgO surface, forming Se-Rh bonds at a distance of 0.244 nm. XPS data suggested that the oxidation state of Se in the catalyst is Se-, while Rh is in a nearly metallic state. CO adsorbs on the rhodium atoms bonded to Se, which is contrasted to blocking of the neighboring Rh sites by Se atom observed with usual impregnated Rh catalysts. The structures of the Se-undoped and -doped Rh6 clusters on MgO are presented in relation to the active site of the cluster catalyst. The data indicate an advantage of molecular clusters over impregnated particles in adsorption capability and catalysis. IntroductionMetal clusters have often been used as precursors of supported metal catalysts. The most prevailing advantage for using metal clusters is to prepare dispersed, fine metal particles on inorganic oxides.] It is possible to control the molecular size of cluster particles on supports by changing the number of nuclear metal atoms. Kirlin et al. reported the dependency of catalytic activity

Chemical Vapor Deposition Methods for the Controlled Preparation of Supported Catalytic Materials

“…From TEM observations, the mean particle size is not altered after Se deposition (around 4 nm), and similar observations have been made for silica-supported catalysts. 329 Whatever the support used, ZrO 2 , 328 SiO 2 , 329 or MgO, 330 the addition of Se promotes the hydroformylation of ethene. On zirconia, the activity enhancement is more pronounced for the GPI-D catalyst than for a coimpregnated one.…”

Promoting Effect of Mo on Alcohol Formation in Hydroformylation of Propylene and Ethylene on Mo-Rh/SiO2

“…It has been known that rhodium is the most active catalyst for hydroformylation. Although the catalyst development for the gas-phase [1,2] and liquid-phase [3][4][5][6] hydroformylation has been performed, the additive effect of various components on heterogeneous Rh catalysts has been investigated [7][8][9][10][11][12][13][14][15]. It has been reported that the additives such as Fe, Zn promote the formation of alcohols in ethylene hydroformylation [1,8].…”

Selective formation of 1-propanol via ethylene hydroformylation over the catalyst originated from RhVO4

“…It has been known that rhodium is most active catalyst for hydroformylation reaction. Although the catalyst development for the gas-phase [1,2] and liquid-phase [3][4][5][6] hydroformylation has been performed, the additive effect of various components on heterogeneous Rh catalysts has been investigated [7][8][9][10][11][12][13]. It has been reported that the additives such as Fe, Zn, and Mo promoted the formation of alcohol in ethylene hydroformylation [7][8][9].…”