Ruthenium/zeolite

Comparison of Initial Methanation Activities for Zeolite and Alumina Supported Ruthenium Catalysts 

Catalyst Ruthenium loading (wt.%) Average particle size (A) Turnover number (sec-1 x 103, 280 C) 

The same workers (234) also studied the methanation behavior of bimetallic clusters of Ru/Ni and Ru/Cu in zeolite Y. Such clusters can be formed by metals, such as ruthenium and copper which are immiscible as bulk metals (235, 236). The turnover numbers versus bimetallic cluster composition are shown in Fig. 22. Dilution of ruthenium with copper clearly causes a marked decrease in specific activity. This decrease in activity is also accompanied by a decrease in methanation selectivity. This was attributed to an inhibiting effect of copper on the ruthenium hydrogenolysis activity. 

The addition of nickel to ruthenium has a less pronounced effect on the methanation activity. This is hardly surprising since nickel is also intrinsically active for methanation. However, dilution of ruthenium with nickel does result in a marked increase in catalyst stability. A catalyst of composition 0.5% Ru, 2% NiY was more stable than those prepared from the pure metals. This improved stability was attributed to an improved balance between the rates of dissociation of CO and hydrogenation of surface carbon, thereby preventing the formation of excess surface carbon. The data presented indicated that a similar improvement in stability was obtained for 0.5% Ru, 2% Ni on A1203, which demonstrates that this effect is not support sensitive. 

Of particular interest was the fact that the bimetallic cluster catalysts, i.e., RuNiY and RuCuY, had considerably better metal dispersions than the pure NiY and CuY catalysts. Further, the zeolite-supported bimetallic catalysts were more resistant to sintering during methanation than those supported on alumina. Particle-size measurement indicated, however, that most of the bimetallic clusters were too large to be located inside the zeolite pores. 

---

Aromatic Gasoline From Hydrogen/Carbon Monoxide Over Ruthenium/Zeolite Catalysts... 

SYNGAS CONVERSION OVER RUTHENIUM/ZEOLITE CATALYSTS AT 51 atm,... 

Fig. 11. Dependence of the catalytic activity (turnover number) of ruthenium A, X, Y, L, and mordenite zeolites for the hydrogenation of benzene on the surface area S of the ruthenium zeolite O, mordenite-4 , A-2 A, X-l A, X-2 0, Y-I . Y-4 , L-2 3, L-4. (Reproduced from Ref. 115 with permission from the authors.)...

Investigations into these topics are presented in this volume. Iron, nickel, copper, cobalt, and rhodium are among the metals studied as Fischer-Tropsch catalysts results are reported over several alloys as well as single-crystal and doped metals. Ruthenium zeolites and even meteo-ritic iron have been used to catalyze carbon monoxide hydrogenation, and these findings are also included. One chapter discusses the prediction of product distribution using a computer to simulate Fischer-Tropsch chain growth. 

Carbon Monoxide Hydrogenation over Ruthenium Zeolites... 

Carbon monoxide is hydrogenated over ruthenium zeolites in both methanation and Fischer-Tropsch conditions. is exchanged in the zeolite as the amine complex. The zeolites used are Linde A, X, Y, and L, natural chabazitey and synthetic mordenite from Norton. The zeolites as a support for ruthenium were compared with alumina. The influence of the nature of the zeolite, the ruthenium metal dispersion and the reaction conditions upon activity and product distribution were investigated. These zeolites are stable methanation catalysts and under the conditions used show a narrow product distribution. The zeolites are less active than other supports. Sintering of ruthenium metal in the zeolite supercages shows only minor effects on methanation activity, although under our Fischer-Tropsch conditions more C2 and C3 are formed. 

The ruthenium zeolites were prepared by conventional ion exchange techniques using the Ru(NH3)e complex. The complex was decomposed at 300°C under flowing dry helium and the catalyst was reduced further under hydrogen at different temperatures. The nickel on NaY zeolite was prepared by conventional ion exchange procedures (9). The sample was dried and hydrogen reduced at 400°C. 

Kinetics. The kinetic data obtained in a differential reactor over the ruthenium zeolites are consistent with the reaction scheme of Vannice and Ollis (17). In this treatment, the rate-limiting step is located in the hydrogenation of an absorbed CHOH species. In the rate expression ... 

Fischei>-Tropsch (F.T.) Activity. Carbon monoxide also was hydrogenated over ruthenium zeolites under F. T. conditions low reaction temperature (>260°C), low CO/H2 ratios (=1), and longer contact times. The catalysts used were 6.6 and 8.6 wt % Ru on Y and X zeolite, respectively. 

Ruthenium zeolites are active and stable methanation catalysts. Under the Fischer-Tropsch conditions used here they show a narrow product distribution. When the size of the ruthenium particles enclosed in the zeolite cages is increased, there is hardly any eflFect found on the methanation activity. Under F. T. conditions a higher amount of C2 and C3 products are formed. Zeolites are generally less active than other supports. In the class of zeolite supports, the less acidic zeolites act as promoters of the CO hydrogenation under methanation conditions the... 

Magnetic and Mdssbauer Characterization of Iron-Zeolite and Iron and/or Ruthenium on Doped-Carhon Catalysts... 

We report here results related to the catalytic behaviour of dodecacarbonyl-tri-iron and tri-ruthenium, bis(cyclopentadienyl-dicarbonyliron) and octacarbonyl-di-cobalt deposited on Y-zeolites under F-T conditions. The influence of the nature of the zeolite and of the metal, the dispersion of the metal and the reaction conditions upon activity and products distribution were investigated. 

Fischer-Tropsch synthesis could be "tailored by the use of iron, cobalt and ruthenium carbonyl complexes deposited on faujasite Y-type zeolite as starting materials for the preparation of catalysts. Short chain hydrocarbons, i.e. in the C-j-Cq range are obtained. It appears that the formation and the stabilization of small metallic aggregates into the zeolite supercage are the prerequisite to induce a chain length limitation in the hydrocondensation of carbon monoxide. However, the control of this selectivity through either a definite particle size of the metal or a shape selectivity of the zeolite is still a matter of speculation. Further work is needed to solve this dilemna. 

The incorporation of a ZSM-5 class zeolite into a ruthenium Fischer-Tropsch catalyst promotes aromatics formation and reduces the molecular weight of the hydrocarbons produced. These composite catalysts can produce a high octane aromatic gasoline in good yield in a single step directly from synthesis gas. 

There are several examples of one-pot reactions with bifunctional catalysts. Thus, using a bifunctional Ru/HY catalyst, water solutions of corn starch (25 wt.%) have been hydrolyzed on acidic sites of the Y-type zeolite, and glucose formed transiently was hydrogenated on ruthenium to a mixture of sorbitol (96%), mannitol (1%), and xylitol (2%) [68]. Similarly a one-pot process for the hydrolysis and hydrogenation of inulin to sorbitol and mannitol has been achieved with Ru/C catalysts where the carbon support was preoxidized to generate acidic sites [69]. Ribeiro and Schuchardt [70] have succeeded in converting fructose into furan-2,5-dicarboxylic acid with 99% selectivity at 72% conversion in a one-pot reaction... 

Ruthenium Tris-bypyridine/Zeolite-Y/Titanium Dioxide Nano-Assembly Ship-in-a-Bottle Synthesis and Applieation in Heterogeneous Photodegradation of 2,4-xylidine... 

---