Cobalt zeolites

Tricarbonyl(naphthalene)chromium, 19 Trimethylsilyl chlorochromate, 327 Cobalt Compounds Acylcobaltate complexes, 101 [Bis(salicylidene-y-iminopropyl)methyl-amine]cobalt(II), 41 Cobalt(II) chloride, 249 Cobalt zeolites, 296 Dicarbonylcyclopentadienylcobalt, 96 Di- x-carbonylhexacarbonyldicobalt,... 

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... 

Propylene Hydroformylation Data Obtained Using Various Cobalt Zeolites ... 

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). 

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 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). 

Besides stmctural variety, chemical diversity has also increased. Pure silicon fonns of zeolite ZSM-5 and ZSM-11, designated silicalite-l [19] and silicahte-2 [20], have been synthesised. A number of other pure silicon analogues of zeolites, called porosils, are known [21]. Various chemical elements other than silicon or aluminium have been incoriDorated into zeolite lattice stmctures [22, 23]. Most important among those from an applications point of view are the incoriDoration of titanium, cobalt, and iron for oxidation catalysts, boron for acid strength variation, and gallium for dehydrogenation/aromatization reactions. In some cases it remains questionable, however, whether incoriDoration into the zeolite lattice stmcture has really occurred. 

It is also important to point out that pure cobalt oxide, alone or finely dispersed in Si02 (i.e. Co-Si02, Co-Si02-l and Co-Si02-2 in Table 1), zeolite HY, fullerene (i.e. C q/C-,0 80/20) is at least as effective as the reduced oxides for the production of nanotubules in our experimental conditions. In fact, the catalysts studied in this work are also active if the hydrogenation step is not performed. This important point, is presently being investigated in our laboratory in order to elucidate the nature of the active catalyst (probably a metal carbide) for the production of nanotubules. 

Vinyl chloride is an important monomer for polyvinyl chloride (PVC). The main route for obtaining this monomer, however, is via ethylene (Chapter 7). A new approach to utilize ethane as an inexpensive chemical intermediate is to ammoxidize it to acetonitrile. The reaction takes place in presence of a cobalt-B-zeolite. 

For infrared spectroscopy, 20-50 mg of the cobalt-exchanged zeolite was pressed into a self-supporting wafer and placed into an infrared cell similar to that described by Joly et al. [21], Spectra were recorded on a Digilab FTS-50 Fourier-transform infrared spectrometer at a resolution of 4 cm-i. Typically, 64 or 256 scans were coadded to obtain a good signal-to-noise ratio. A reference spectrum of Co-ZSM-5 in He taken at the same temperature was subtracted from each spectrum. 

Based on previous studies [15, 22-25], the band at 1941 cm-i is assigned to Co2+(NO), and the pair of bands at 1894 and 1815 cm-i, to Co2+(NO)2- The shoulders at 1874 and 1799 cm may be due to a second dinitrosyl species. While little is known about the location and coordination of the Co 2+ in ZSM-5, it is likely that cobalt ions are associated with both [Si-0-Al]- and [Al-0-Si-0-AI]2- structures in the zeolite. In the former case, the cobalt cations are assumed to be present as Co2+(OH-) cations and in the latter case as Co2+ cations. The presence of cobalt cations in different environments could account for the appearance of two sets of dinitrosyl bands. The band at 2132 cm-> is present not only on Co-ZSM-5 but also on H-ZSM-5 and Na-ZSM-5, and has been observed by several authors on Cu-ZSM-5 [26-28]. 

Pietrzyk, P., Sojka, Z. (2007) Co2+/Co° redox couple revealed by EPR spectroscopy triggers preferential coordination of reactants during SCR of NOx with propene over cobalt-exchanged zeolites, Chem. Commun., 1930. 

Montanari, T., Marie, O., Daturi, M. et al. (2005) Cobalt on and in zeolites and silica-alumina Spectroscopic characterization and reactivity, Catal. Today, 110, 339. 

It corresponds to the cobalt initially exchanged into the HMOR porosity. Nevertheless, a fraction of cobalt oxide - Co304 - is produced after calcination, as previously seen in the case of Cat I, on the surface of zeolite grains. 

The present study concerns the interaction of propene molecules with cobalt sites in CoZSM-5. The experiments of CO and NO sorption evidenced that this zeolite contained practically only Co2+ in exchange position and Co3+ in oxide form. Propene is a reactant in several reactions catalyzed by cobalt containing zeolites (like reduction of NO, amonoxidation of propene and others). 

The existence of small quantities of zeolite in Y-AI2O3 was verified by X-Ray diffraction with the K ray of cobalt, especially for the samples with the smallest contents of zeolite. 

Figure 1 shows the H2-TPR profiles of Co- and Co/Pd-HFER catalysts. The H2-TPR profile of Co-HFER shows the presence of two peaks at 340 °C and 670 °C corresponding to the reduction peaks of particles of cobalt oxides (Co304 and CoOx respectively). Normally, Co304 are on the external surface while CoOx is inside the zeolite cavities [11-13], At 960 °C, the reduction of the cationic species Co2+ occurs [14]. 

In addition to other polystyrene [138] and silica supports [139, 140, 141, 142, 143,144], iron and cobalt precatalysts have been immobilised on calcosilicate [145], magnesium dichloride [146,147,148,149], MCM-41 zeolite [150,151], clay [152] and fluorotetrasilicic mica [153], Supported systems have also been examined using alternative activators [154, 155, 156, 157, 158, 159]. For example, silica- and alumina-supported samples 5 have been activated with AK/ -Bu), to afford highly active, thermally robust catalysts [154], IR spectroscopy in DRIFT mode... 

---