Supported Sn-Ru Catalysts

It is interesting to note that the ruthenium-tin boride system exhibited unique properties in the hydrogenation of cinnamaldehyde to unsaturated alcohol. In addition, very good results have been obtained with tin promoted ruthenium catalysts in the hydrogenation of different unsaturated aldehydes.  

Mendes et aC have studied the performance of different supported ruthe- 

The enhanced activity of transition metal catalysts supported on reducible oxides in the selective hydrogenation of the C=0 bond is generally attributed to 

It is known that an oxide support can strongly interact with another supported oxide, affecting its reducibility, and that the stability of supported oxides is determined by the similarity of the electronegativities of the two cations. It is interesting to note, in this context, that in activated Sn-Pt/Si02 and Sn-Ru/Si02 catalysts tin is mainly present as metallic Sn° and as metal-tin alloys, while in activated Sn-Pt/AbOB and Sn-Ru/AbOa tin is otherwise stabilized as It is 

It is also worthwhile mentioning that Barbier et al. have prepared and characterized rutheniun-tin mixed oxide catalysts used in electro-oxidation of phenol. XRD of the calcined catalysts revealed the presence of RUO2, Sn02 and some trace amount of metallic ruthenium. However, there was no evidence of the formation of solid solutions of oxides.  

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Scheme 5 Mechanism of the hydrogenation of methyl oleate into oleyl alcohol via the formation of aldehyde over alumina supported Sn-Ru catalyst (Reproduced from ref. 72 with permission)...

Besides oxide supported Sn-Ru catalysts, carbon supported catalysts also find application in hydrogenation reactions. Sn Mossbauer spectroscopy was used to investigate the tin component of ruthenium and tin supported on activated carbon catalysts containing 2 wt. % ruthenium and having Sn/(Sn-f Ru) ratios between zero and 0.4. Four major components in the Sn Mossbauer spectra were attributed to both Sn(II) and Sn(IV) oxides and to Ru-SnOx species formed on the surface of ruthenium metal particles. In addition to this " Sn spectra reveal the presence of minor amounts of Ru3Sn7 alloy phase. ... 

Despite the extended studies on supported Sn-Ru catalysts used in different selective hydrogenation reactions and hydrogenolysis of esters there is a need to further investigate the effect of catalyst preparation and pretreatment parameters on the performance of this bimetallic system. 

Alumina (CK-300 Ketjen y-AbOs, S = 180 m g) supported Sn-Ru catalysts were prepared by co-impregnation or successive impregnation. Various metal precursor salts were used RUCI3XH2O, Ru(acac)3, SnCbx2H20, Ci2H2404Sn... 

Alumina supported Sn-Ru and Re-Pt catalysts were found to be highly active and selective in liquid phase hydrogenolysis of ethyl dodecanoate and butyl acetate to the corresponding alcohol. The content of ionic forms of the second metals strongly affected the performance of these catalysts. The interaction between two metals in these catalysts has been shown by different experimental methods. 

Various metals/metallic oxides have been coated onto carbons with the aim to improve the platinum tolerance to poisons, increase the platinum utilization and to avoid carbon corrosion of the catalyst support. Sn, Ru, Ti, and Co metals as well as their oxides have been reported on in fair amounts as being transition metals capable of increasing the platinum utilization by removing hydroxide species that would be present on the platinum such that the platinum can further catalyze the ORR. Although these materials have been coated onto the carbon as a support, there are alloying characteristics that occur with the impregnated platinum which result and thus will not be touched up in this section. However, many of these oxides and metals have been used as stand-alone catalyst supports without the use of a carbon substrate, and are discussed further in Section 3.5.3. 

Hydrogenolysis of esters to aldehydes or alcohols needs high temperatures and high pressures. Moreover, it leads to the formation of acids, alcohols, and hydrocarbons. In contrast, bimetallic M-Sn alloys (M = Rh, Ru, Ni) supported on sihca are very selective for the hydrogenolysis of ethyl acetate into ethanol [181]. For example while the selectivity to ethanol is 12% with Ru/Si02, it increases up to 90% for a Ru-Sn/Si02 catalyst with a Sn/Ru ratio of 2.5 [182]. In addition, the reaction proceeds at lower temperatures than with the classical catalysts (550 K instead of temperatures higher than 700 K). The first step is the coordination of the ester to the alloy (Scheme 46), and most probably onto the tin atoms. After insertion into the M - H bond, the acetal intermediate decomposes into acetaldehyde and an ethoxide intermediate, which are both transformed into ethanol under H2. 

At this stage, it should be pointed out that modihcation of a Pt-Sn catalyst by Ru atoms increases cell performance (and hence catalytic activity with regard to ethanol electro-oxidation), but has no effect on the OCV or on product distribution [Rousseau et al., 2006]. It seems, then, that the oxidation mechanism is the same on Pt-Sn and Pt-Sn-Ru, which supports the proposition that Ru allows OH species to be produced when the anode potential is increased and noncatalytically active tin oxides are formed. 

Supported metallic Ni, Cr, Fe, Mo, Co, V, Ti, Sn, Ru, and Pd catalysts have been prepared with the help of the CVD method fundamentally using carbonyl and chloride precursors [16]. 

A.S. Arico, Z. Poltarzewski, H. Kim, A. Morana, N. Giordano, V. Antonucci, Investigation of a carbon supported quaternary Pt-Ru-Sn-W catalyst for direct methanol fuel cells. J. Power Sources 1995, 55(2), 159-166. 

Electrodes The porous electrodes consist of carbon cloths loaded with a mixture of platinum and Nafion. In order to achieve a good contact between the electrode, the catalyst, and the electrolyte, the electrodes are pressed on the electrolyte membrane, which acts as the supporting component. Other catalysts such as binary Pt-Ru mixtures and ternary systems such as Pt- Ru- Sn have been studied for better CO tolerance [8]. The current density voltage curves of Fig. 7 show the effect of CO on the performance of a cell with platinum as catalyst. Fig. 8 shows the higher catalytic... 

The effect of Sn Ru atomic ratio on the XRD spectra of alumina supported bimetallic catalysts is shown in Figure 34. As seen the higher the Sn Ru ratio... 

Summary on Sn-Ru/AkO Catalysts. - In the last decade supported tin-ruthenium catalysts have been extensively studied because of their activity and high selectivity in the hydrogenation of unsaturated aldehydes, esters or acids into the corresponding alcohols. The increased performance of metal catalysts with the addition of promoters such as tin is attributed to the presence of promoter-cations on the surface or at the periphery of metal nanocluster, which activate the C=0 bond through the interaction with the lone electron pair of the carbonyl group oxygen. 

It has been shown that new types of supported Au, Cu, Sn-Pt, Sn-Ru, Re-Pt, catalysts have been prepared and used for selective hydrogenation of different organic carbonyl compounds (unsaturated aldehydes, esters, carboxylic acids, carboxamides, etc.) and nitriles. Supported Sn-Pt and Au catalysts were also... 

Jozef Margitfalvi and Sandor Gobolds (Hungarian Academy of Sdences, Budapest, Hungary) provide a comprehensive review of the interaction of metal and metal ions in nanoscale clusters. They show that there are unique catalytic properties derived from the molecular interaction of these types of clusters. Their review summarizes the literature on five case studies that exemplify this type of interaction Sn-Pt, supported Au, Sn-Ru, Re-Pt, and several Cu-containing catalysts. They discuss both oxidation and hydrogenation reactions on these types of catalysts, and provide detailed summaries of the literature, as well as examples from research in their own labs. 

Antolini E, Cohnatia F, Gonzalez ER (2007) Effect of Ru addition on the structural characteristics and the electrochemical activity for ethanol oxidation of carbon supported Pt-Sn alloy catalysts. Electrochem Commun 9 398 04... 

The previous examples are all supported gold catalysts. Supported bimetallic catalysts have been explored as well. Scurrell and coworkers developed a series of Au-M/ Fe Oj (M=Ag, Bi, Co, Cu, Mn, Ni, Pb, Ru, Sn, Tl) catalysts for WGS [70,71], These catalysts were prepared by deposition-coprecipitation using HAuCl, FeCNOjjj, and metal salts as precursors, followed by calcination in air at 400°C. Au-Ru/Fe Oj showed the highest activity. However, there is no evidence showing that the so-called bimetallic catalysts are bimetallic. The thermal decomposition of metal salts in air usually leads to the formation of metal oxides instead [61]. 

Further reaction of CO and/or CO2 with H2 would lead to methanation or Fischer-Tropsch reactions [125]. The selectivity towards hydrogen or alkanes can be adjusted by the choice of the active metal and the supports of the catalysts. In this way, higher selectivities towards hydrogen could be achieved if Pt, Ni, and Ni-Sn are used on alumina and titania as support material, whereas Ru, Rh, and Ni and also Si02—AI2O3 as support revealed higher alkane selectivities [124,126]. 

Coq, B., Kumbhar, P. S., Moreau, C., Moreau, R, Figueras, F. (1994) Zireonia-supported monometallic Ru and bimetallic Ru-Sn, Ru-Fe catalysts role of metal support interaction in the hydrogenation of cinnamaldehyde. y. Phys. Chem. 98(40), 10180-10188... 

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