J.J.F. Scholten

Partial liquid phase hydrogenation of benzene to cyclohexene over ruthenium catalysts in the presence of an aqueous salt solution: I. Preparation, characterization of the catalyst and study of a number of process variables

Abstract A study has been made of the batch-wise partial hydrogenation of benzene to cyclohexene over ruthenium catalysts in the presence of an aqueous zinc sulphate solution. The reaction was performed at 423 K and at a pressure of 5.0 MPa in a stirred autoclave. The influence of a number of process variables on the performance of the catalyst, like the presence of water, the presence of salt-additives, the stirring speed, the temperature, the hydrogen pressure, the amount of catalyst, the catalyst particle size and the benzene/water ratio have been studied. It was found that it is extremely important that the catalyst is hydrophilic and therefore surrounded by a stagnant water layer; the presence of a stagnant water layer results in the suppression of the reaction rate and in a strong increase of the cyclohexene selectivity and yield. The high yield of the intermediate product, cyclohexene, which is of the order of 40 to 50 mol-%, is attributed to a physical effect, in casu severe mass transport limitation. Mass transfer calculations strongly support this conclusion.

Selectivity to cyclohexenes in the liquid phase hydrogenation of benzene and toluene over ruthenium catalysts, as influenced by reaction modifiers

Abstract A study has been made of the selective liquid-phase hydrogenation of benzene and toluene to cyclohexene and methyl-substituted cyclohexenes, respectively, at ambient temperature and pressure. Just as in gas-phase hydrogenation, the selectivities to cyclohexene or to substituted cyclohexenes strongly increase when reaction modifiers are added. Compounds exhibiting a reaction modifying action contain a hydroxyl or an amine group. The action of modifiers in the liquid phase is explained along the same lines of reasoning as advanced for the case of gas-phase hydrogenation (P.J. van der Steen and J.J.F. Scholten, Appl. Catal., 58 (1990) 291 and J. Struijk and J.J.F. Scholten, Appl. Catal., 62 (1990) 151), and is based on the formation of a hydrogen bond between cyclohexene and the modifier. In the hydrogenation of toluene a large difference in the selectivity to 1-methylcyclohexene and 3- and 4-methylcyclohexene is observed. An interpretation of this effect is presented.

Hydroformylation with supported liquid phase rhodium catalysts Part I. General description of the system, catalyst preparation and characterization

Abstract Hydridocarbonyltris(trihenylphosphine)rhodium(I) dissolved in triphenylphosphine and capillary condensed in the pores of a support material, is applied in the heterogeneous hydroformylation of propylene at 90 °C and 1.57 MPa total pressure. The activity and selectivity of this new catalyst are high compared with those of known analogues. No sign of deactivation is observed over a period of more than 800 h. A small weight increase of the catalyst used is occasionally observed, and is attributed to some accumulation of low-volatile aldol condensation products in the pores. The aldol condensation reaction can be suppressed by using macroreticular polystyrene-divinylbenzene, XAD-2, or sodium-poor silica as support material. New bands in the IR spectrum of rhodium complexes are detected at 1947, 1993, 2002 and 2070 cm −1 , which cannot be assigned to known rhodium complexes. Nitrogen capillary condensation proves the catalyst solution at 56% pore filling to be mainly located in the smallest pores of the support. X-ray microanalysis reveals a rather uniform distribution of the catalyst solution across a catalyst particle.

Gas phase hydroformylation of propylene with porous resin anchored rhodium complexes part I. Methods of catalyst preparation and characterization

Abstract Hydridocarbonyltris(triphenylphosphine)rhodium(I) anchored to the surface of macroreticular polystyrene—divinylbenzene is applied in the heterogeneous hydroformylation of propylene at 90 °C and 0.1 MPa total pressure. The performance of the catalyst depends on the method of preparation. We finally succeeded in preparing highly stable, active and selective catalysts. The methods of functionalization of the support with phosphine and phosphite ligands by means of chloromethylation and chlorophosphonation are studied and correlated with the performance of the catalyst. The method of coupling of the rhodium complex to the functionalized support influences the activity and selectivity of the catalyst. Laser Raman spectroscopy showed the presence of a high content of unpolymerized vinyl groups. Functionalization of the resin lowers the amount of vinyl groups substantially, which is supported by the results of a specific reaction with iodine chloride. The texture of the catalyst was studied by physical adsorption and capillary condensation of nitrogen and is discussed in relation to the preparation of the catalyst.

Hydroformylation with supported liquid phase rhodium catalysts Part III Influence of the type of support, the degree of pore filling and organic additives on the catalytic performance

Abstract Hydridocarbonyltris(triphenylphosphine)rhodium(I), dissolved in triphenylphosphine and captivated in the pores of a support by strong capillary forces, is applied in the heterogeneous hydroformylation of ethylene and propylene. The activity of this supported liquid phase rhodium catalyst is highly dependent on the type of support and the degree of pore filling, owing not only to a variation in surface area of the gas-PPh3 phase boundary, but also to a variation in the degree of adsorption of the rhodium complexes onto the support surface. The long activation time of the catalyst on certain silicas and silica—alumina is due to a slow increase of the complex concentration in the PPh3 caused by slow desorption of the rhodium complexes from the support surface, and by additional spreading of the catalyst solution over the support. Both phenomena are induced by a small quantity of aldol condensation products slowly formed by consecutive reactions of the produced aldehydes. The activation time of the catalyst is appreciably shortened and the activity and selectivity increased, by previous addition of aldol condensation products or polyethylene glycol to the catalyst solution, or by modification of the silica surface with tri(ethoxy)phenylsilane.

Stability of copper/cobalt catalysts for the synthesis of higher alcohols from syngas

Abstract The stability of two ZnO/Al 2 O 3 -supported copper/cobalt catalysts for higher alcohol synthesis, a KOH-promoted and a non-promoted one, have been studied in a Berty reactor for respectively 1600 and 4200 h. Both the fresh and spent catalysts were analyzed using various techniques. The spent catalysts show a strong lowering of the BET and free-metal surface areas and X-ray diffraction data reveal the presence of Co 2 C and ZnO in addition to metallic copper and the formation of a spinel phase. Elemental analysis of the spent catalysts shows an increased carbon content and a lowering of the sodium and/or potassium content. Furthermore, spent catalysts contain substantial amounts of adsorbed heavy hydrocarbons, water and coke. The coke is not completely removed by a hydrogen treatment at high temperatures. It appears that the ZnO-enriched zinc oxide-alumina support deteriorates during higher alcohol synthesis into ZnO and a ZnO-poor zinc oxide-alumina phase. This last effect is more severe for the potassium-doped catalyst. The gradual deterioration of the support and of the copper-cobalt crystallites is irreversible; regeneration by the reduction of the spent catalyst appeared to be ineffective.

Hydroformylation with supported liquid phase rhodium catalysts Part V. The kinetics of propylene hydroformylation

Abstract We studied the kinetics of the heterogeneous hydroformylation of propylene, using hydridocarbonyltris(triphenylphosphine)rhodium(I), dissolved in triphenylphosphine and capillary condensed into the pores of a support, as a catalyst. The results can be described by the power rate equation: where Ea, the apparent activation energy, is equal to 79.1 kJ/mol, and the reaction orders a, b and c are 1.03, 0.09 and 0.23, respectively. The reaction order in carbon monoxide c is pressure dependent, and at carbon monoxide pressures above 0.15 MPa equal to 0.08. The selectivity towards n-butyr-aldehyde is not influenced by the hydrogen and propylene pressures, but varies strongly with the partial pressure of carbon monoxide. When this partial pressure is lowered from 0.52 to 0.05 MPa, the selectivity increases from 10 to 30. Similarly, an increase in temperature from 70 to 106.8 °C raises the selectivity from 6.7 to 11.5. With Kieselguhr and polystyrene—20% divinylbenzene (XAD-2) as catalyst supports, the rate of reaction is first order in rhodium complex concentration in the solvent ligand PPh3. The kinetics differ significantly from those found in homogeneous hydroformylation in, for instance, toluene.

Hydroformylation with supported liquid phase rhodium catalysts Part IV. The application of various tertiary phosphines as solvent ligands

Abstract The heterogeneous catalytic hydroformylation of propylene is carried out at 90 – 199 °C and 1.57 MPa total pressure, over a supported liquid phase rhodium catalyst. In addition to triphenylphosphine, various other tertiary phosphines may be used as solvent ligands. It turned out that tri(p-tolyl)-phosphine, tri(2-cyanoethyl)phosphine and S(+)−(2-phenylbutyl)diphenyl-phosphine are very attractive solvent ligands, since they provide the catalysts with excellent stability and selectivity, and satisfactory activity. The volatility of these ligands being relatively low, the supported liquid phase rhodium catalysts can be applied at temperatures up to ∼ 140 °C, without severe loss of phosphine by evaporation. Above 150 °C deactivation of the catalysts is observed; this is thought to be due to metallation of the coordinated ligands by the rhodium metal.

Hydroformylation with supported liquid phase rhodium catalysts Part II. The location of the catalytic sites

Abstract Hydridocarbonyltris(triphenylphosphine)rhodium(I), dissolved in triphenylphosphine and capillary condensed into the pores of a support, is applied in the catalytic heterogeneous hydroformylation of ethylene and propylene. Catalysts with triphenylphosphine in the liquid and in the solid state, do not show any difference in apparent activation energy and catalytic activity. From this it follows that we are dealing with a case of heterogeneous catalysis, i.e. that only the rhodium complexes at the gas-triphenylphosphine phase boundary are involved in the reaction. The inactivity of the rhodium complexes outside the phase boundary is most likely due to high coordination of these complexes with free triphenylphosphine molecules, and to the very low solubility of carbon monoxide in triphenylphosphine, and not to an extreme liquid-phase diffusional retardation of the rate of reaction.

Gas phase hydroformylation of propylene with porous resin anchored rhodium complexes part II. the catalytic performance

Abstract Hydridocarbonyltris(triphenylphosphine)rhodium(I), chemically anchored via phosphine or phosphonite ligands to the surface of macroreticular polystyrene divinylbenzene, is successfully applied in the heterogeneous gas phase hydroformylation of propylene at 90 °C and 0.1 MPa total pressure. Catalysts prepared via chlorophosphonation are stable; at a conversion of 0.9% no deactivation is observed over a period of more than 500h. Catalysts prepared via chloromethylation deactivate slightly, but have a higher selectivity for n-butyraldehyde than those prepared via chlorophosphonation. The hydroformylation activity per unit weight of rhodium, for catalysts with anchored diphenylphosphines prepared via chlorophosphonation, decreases with increasing phosphorus ligand coverage. Addition of a small amount of triphenylphosphine to catalyst with chemically anchored ligands raises the selectivity for n-butyraldehyde formation. The influence of the type of anchored ligand on the catalytic performance will be discussed.