Cobalt zeolite catalysts

Catalyst Characterization. Chemical analyses, x-ray diifraction analyses, and gas adsorption procedures were used to characterize the composition, crystallographic character, and surface structure of the nickel and cobalt zeolite catalyst preparations. The chemical and x-ray procedures were standard methods with the latter described elsewhere 11). Carbon monoxide chemisorption measurements provide useful estimates of the surface covered by nickel atoms from the zeolite substrate 10). 

The performance of several of the nickel and cobalt zeolite catalysts for steam reforming of n-hexane at 400°-500°C has been evaluated by short test runs with the reactor and the procedures described above (Table II). A Girdler reforming catalyst (G56) was tested under the same conditions as a comparative standard. All tests were conducted at a total pressure of 1 atm. Plateaus of sustained reforming activity were established within 1 hour. The cobalt catalysts lost essentially all reforming activity within 3 hours, presumably because of oxidation by steam. The space velocities reported are calculated in terms of theoretical hydrogen production based on the n-hexane injection rate and extent of conversion (Equation 2, Table II). The equation for the steam reforming of n-hexane with complete conversion to carbon dioxide is... 

During investigation of cobalt-zeolite catalysts the dependence of activity on the manner by which the active phase was introduced was established. Sample of 10% CoO/H-TsVN (Si02/Al203=37) (in which cobalt was introduced by soaking) had low activity in the selective catalytic reduction of NO with CH. Conversion of 25% of NO was achieved at 320 °C, which is considerably lower than for cobalt containing cation-decationated form of zeolite with the pentasil structure, obtained by ion exchange in the solid phase (e.g., on Co-H-TsVN an 80% conversion of NO was obtained at 310 °C) [8]. 

The use of a copper exchanged H-ZSM-5 zeolite (Cu-ZSM-5) has been reported for the production of acetic acid and methyl acetate from methanol (87). Copper incorporated into H-ZSM-5 performs better at 70 atm pressure and 285-375°C compared to 10 atm (76), but the space time yield or productivity of acetyls (acetic acid -l-methyl acetate) is low, at about 0.03 g/(gcat. h) and the maximum selectivity is 17% at 33% methanol conversion. Higher productivities have been reported for cobalt/zeolite catalysts but pressures of approximately 700 atm are needed (88). 

The study carried out by Centola et al. (225) was apparently stimulated by a patent (227) in which cobalt zeolites X and Y were claimed as catalysts... 

Tailoring of the product distribution is possible by a limitation of chain growth by pore size. This has been demonstrated by Ballivel Tkatchenko and Tkatchenko using zeolite catalysts. Ruthenium, iron or cobalt metal particles in Y-zcolilc supcrcagcs were prepared by thermal decomposition of the carbonyls. These metal-zeolite catalysts give selective formation of )- hydrocarbons [471. 

For ferromagnetic cobalt particles in zeolite X, spin-echo ferromagnetic resonance has been used to obtain unique structural information (S6). In addition, study of the catalytic signature of metal/zeolite catalysts has been used by the groups of Jacobs (87), Lunsford (88), and Sachtler (47,73,89). Brpnsted acid protons are identified by their O—H vibration (90,91) in FTIR or indirectly, by using guest molecules such as pyridine or trimethylphosphine (92,93). An ingenious method to characterize acid sites in zeolites was introduced by Kazansky et al., who showed by diffuse reflection IR spectroscopy that physisorbed H2 clearly discerns different types of acid sites (94). Also, the weak adsorption of CO on Brpnsted and Lewis acid sites has been used for their identification by FTIR (95). The characterization of the acid sites was achieved also by proton NMR (96). 

The Beckmann rearrangement of ketoximes to the corresponding amides (31), the Fischer indole cyclization, isomerization of epoxides to the corresponding aldehydes, ketones, or alcohols, hydration and ammo-nolysis of epoxides, oxygen-sulfur interchange, formation of diaryl-ureas and -thioureas from condensation of aniline and carbonyl sulfide, and olefin carbonylation occur over zeolite catalysts (62). The oxo reaction over rhodium and cobalt containing zeolites recently has been claimed (22). 

Catalyst Composition. Chemical compositions of typical nickel and cobalt zeolites are summarized in Table 1. Based on the total CEC derived from the initial sodium composition, 23 to 37% of the Zeolon and 8.4% of the Linde SK400 exchange sites are occupied by nickel cations. In Zeolon, 55% of the exchange sites are occupied by cobalt cations. A ratio of 1.41 1 for cobalt to nickel on the Zeolon exchange sites resulted where nickel and cobalt were exchanged under comparable conditions. 

The basic approach to prepare Co(II)-complexes of salen (N,lSr-bis(salicylidene)ethylene-diamine)-type molecules is the flexible ligand method [9]. In this process the Schiffbase ligand can diffuse by twisting into the zeolite where it becomes too large to exit by complexation with the cobalt ion. The flexible ligand method, however, was not usefiil for the preparation of Co-salophen/ zeolite catalyst, because the product was inactive in the oxidation reactions. The salophen molecule does not seem to be flexible enough and can not get into the zeolite to produce the suitable complex in the supercage. 

The cobalt supported zeolite catalyst was prepared by ion exchange. Powdered zeolite A was slurried in distilled water, and an aqueous solution of Co(N0j)2.6H20 was added dropwise over a period of five hours with stirring and gentle heating. The saiple was then filtered and air dried at room temperature. 

The activities of the cobalt supported catalyst for Fischer-Tropsch synthesis are summarised in Fig. 2 in terms of yields of Cj to C3 hydrocarbons. Only data at 250°C and 325°C are presented although other temperatures have been examined. The cobalt on IfeO, on the zeolite support, and on the blank supports alone, were inactive. The same groupings occurred with respect to CO consumption in the TPC runs. 250° C... 

The Co/zeolite catalyst (Fig. If) was reduced only to the extent of 60 wt% at 800°C. The unreduced cobalt is attributed to tetrahedral Co2+ species (phase III) since they exhibited the characteristic intense blue colour of tetrahedral Co2+ ions. The cobalt on magnesiun oxide (Fig. lg) also underwent reduction to only 60wt% up to 800°C. The shift of the phase II and III peaks to higher temperatures is evidence of a stronger metal-support interaction for these catalyst systems. Itoo reduction phases for cobalt on magnesium oxide have been... 

The zeolite catalysts were prepared by ion-exchange of NaY (Aldrich, Si/Al 2.7) with measured amounts of the relevent metal compounds (chromium acetate and cobalt nitrate). In a typical procedure 10 g of the zeolite was dispersed in 500 ml of dionized water. The metal salt solution was added dropwise to this vigorously stirred mixture, after which the mixture was stirred overnight, followed by filtering and drying of the material at 1(K) C. Chemical analysis of the samples (XRF) indicated the presence of 10 wt% Co in CoNaY-1 and 4 wt Cr in CrY. 

In this communication we wish to report a new, mild, aerobic oxidation of alcohols, catalyzed by ruthenium and cobalt(salophen)/zeolite catalysts. 

Cobalt(saiophen) encapsulated in zeolite. The template synthesis method was used for the preparation of the Co(salophen) /zeolite catalyst (salophen = N,N - Bis(salicylidene) -1,2-phenylenediamine). The Co - exchanged zeolite was prepared by stirring 6g of NaY zeolite and 0.9 g of Co(OAc)2 4 H2O, dissolved in 150 ml deionized water for 48 h at room temperature. The slurry was then filtered and the pink solid obtained was washed with deionized water and dried overnight at 523 K. 0.62 g salicylaldehyde was added to 6g of Co-exchanged zeolite. 0.28 g 1,2-phenylenediamine was dissolved in 20 ml of methanol and the solution was slowly added to the mixture of the zeolite and salicylaldehyde. Having added the solution, the reaction mixture was refluxed for 1 hour and then allowed to stand at room temperature overnight. The product was filtered, washed with methanol and dried. 

The commercial process for the production of nylon 6 starts with the oxidation of cyclohexane with oxygen at 160°C to a mixture of cyclohexanol and cyclohexanone with a cobalt(II) catalyst. The reaction is taken to only 4% conversion to obtain 85% selectivity. Barton and co-workers have called this the least efficient major industrial chemical process.240 They have oxidized cyclohexane to the same products using tort bu(ylhydroperoxide with an iron(III) catalyst under air (70°C for 24 h) with 89% efficiency based on the hydroperoxide. The oxidation of cyclohexanol to cyclohexanone was carried out in the same way with 99% efficiency. A cobalt catalyst in MCM-41 zeolite gave 38% conversion with 95% selectivity in 4 days at 70 C.241 These produce ferf-butyl alcohol as a coproduct. It can be dehydrated to isobutene, which can be hydro-... 

Structure-Sensitive Reactions of Cyclopropane with Cobalt and Iron Zeolite Catalysts... 

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