Lars Peter Lindfors

Preparation of Ni/Al2O3 catalysts from vapor phase by atomic layer epitaxy

Ni/Al2O3 catalysts were prepared by saturating gas-solid reactions as an atomic layer epitaxy (ALE) process. Vaporized Ni(acac)2 was chemisorbed on a porous alumina support, and the produced surface complex was then air treated to remove the ligand residues. The nickel content could be precisely controlled by repeating this reactor cycle. On alumina preheated at 800°C, the nickel content varied from 3 to 21 wt%, when the number of reaction cycles was increased from one to ten. The performance of the Ni-catalysts was evaluated in the gas-phase hydrogenation of toluene. The preheat temperature of alumina influenced the activity of the catalyst, and a maximum in the activity was observed for catalysts prepared from alumina preheated at 875°C. Catalysts prepared by four reaction cycles, containing about 10 wt% nickel, gave the highest utilization of nickel.

Chemisorption and TPD studies of hydrogen on Ni/Al2O3

Abstract The activities of two supported nickel catalysts, a commercial (17 wt.-% Ni/Al 2 O 3 ) and a non-commercial (10 wt.-% Ni/Al 2 O 3 ) catalyst, were investigated in gas phase toluene hydrogenation. Both catalysts were active in hydrogenation, exhibiting rate maxima at about 443 K. The catalysts were characterized using hydrogen chemisorption and temperature programmed desorption (TPD) techniques. Decreasing hydrogen adsorption capacity was generally found in the temperature interval 298–423 K, the capacity of both the commercial and the non-commercial Ni-catalysts being about 20 cm 3 /g Ni at 423 K. No effect on the total adsorption capacity was found by increasing the pretreatment temperature from 503 K to 773 K on the commercial catalyst. Three adsorption states of hydrogen (I–III) were resolved from the TPD-spectra of both catalysts. Hydrogen desorption was modelled with peak shape analysis as a second order process with free readsorption, giving hydrogen adsorption enthalpies ranging from −108 to −124 kJ mol −1 for adsorption state I. The kinetic data and the TPD studies indicate that the decrease of the toluene hydrogenation activity at temperatures above 443 K is due to the decay of adsorption state I.

The growth mechanism of nickel in the preparation of Ni/Al2O3 catalysts studied by LEIS, XPS and catalytic activity

A series of Ni/Al2O3 catalysts prepared from vapor phase by the atomic layer epitaxy (ALE) technique have been studied. A model is proposed for the growth mechanism of nickel in its oxidic form on alumina, from sequences of treatments with Ni(acac)2 and air. In the study activity measurements were combined with surface analysis by LEIS and XPS. During the first preparation sequence (< 5 wt% Ni) atomically dispersed nickel is obtained on the alumina support. The nickel atoms are catalytically inactive, but act as nuclei for the growth of the catalytically active Ni-species during the subsequent preparation sequences. The highest utilization of nickel atoms in the hydrogenation of toluene was obtained when the nickel nuclei were covered with one layer of active nickel species.

Kinetics of toluene hydrogenation on Ni/Al2O3 catalyst

The gas phase hydrogenation of toluene to methylcyclohexane on a commercial Ni/Al2O3 catalyst was investigated in a differential reactor operating at atmospheric pressure and temperatures between 150 and 210°C. The results revealed that the hydrogenation kinetics is of the order 1–3 with respect to hydrogen at the actual temperature interval and that the reaction order increases with temperature. The reaction order with respect to toluene is negative. The reaction rate exhibited a maximum at approximately 170°C. The rate maximum is explained by the escape of catalytically active hydrogen from the Ni-surface at the highest reaction temperatures, which was confirmed by temperature-programmed desorption studies and chemisorption studies of hydrogen. The kinetics was modelled with an empirical power-law rate expression and with three mechanistic rate models. The latter were based on the assumption of rapid competitive adsorption steps of toluene and hydrogen and rate determining surface reaction steps involving addition of hydrogen atoms to adsorbed toluene and partially hydrogenated intermediate molecules. The best fit to the experimental data were provided by two models; one implying simultaneous addition of hydrogen atoms to adsorbed toluene and the other, being more probable from a mechanistic point of view, implying sequencial addition of hydrogen atoms to adsorbed toluene.

Activation of Ni/A12O3 catalysts through modification of the Al2O3 support

The effect of alumina pretreatment on the performance of alumina supported nickel catalysts was demonstrated in gas phase hydrogenation of toluene to methylcyclohexane. The state of the alumina was changed from pure γ to pure θ phase through various heat treatments in air. The catalysts were prepared from vapor phase by saturating the accessible binding sites on the pretreated alumina with the nickel precursor. The highest number of active sites for hydrogenation was observed for catalysts prepared on alumina having an incomplete phase transition and a θ/γ alumina phase ratio between 0.5 and 10. Results from temperature programmed desorption (TPD) studies revealed that a maximum in weakly chemisorbed hydrogen as well as in total amount of desorbed hydrogen was found for the same catalysts. By hydrogen chemisorption studies the total hydrogen uptake was found to correlate with the observed hydrogenation maximum. It is suggested that both the chemical and physical properties of the alumina influence the activity. An optimal metal-support interaction and structural defects on the alumina due to the phase transition can explain the observed maximum in the number of active sites and in hydrogen uptake.

Modelling of speciality chemicals production in liquid–liquid reactors—A case study: synthesis of diols

Abstract Generalized mass balance models were derived for semibatch liquid–liquid reactors, which are frequently used in the production of fine and speciality chemicals. The model comprises the reaction kinetics, liquid–liquid equilibria as well as interfacial mass transfer effects. The reactor model was applied on a case study, homogeneously catalyzed synthesis of diols through aldol condensation and Cannizzaro reaction. Rate equations for the process were obtained by applying steady-state approximations on ionic reaction intermediates. The rate equation were incorporated into the mass balances and tested with experimental kinetic data. The model was able to imitate the experimental behaviour of the two-phase system.

Hydrogenation of 2,2-dimethylol-1-butanal and 2,2-dimethylol-1-propanal to trimethylolpropane and trimethylolethane over a supported nickel catalyst

The hydrogenation kinetics of 2,2-dimethylol-1-butanal (TMP-aldol) and 2,2-dimethylol-1-propanal (TME-aldol) over a supported nickel catalyst were determined with experiments carried out in a batchwise operating autoclave at 50−90 °C and 40−80 bar hydrogen. Water was used as the solvent. TMP- and TME-aldol were hydrogenated with 100% selectivity to the corresponding triols. The effects of the catalyst activation procedure and the formaldehyde concentration on the hydrogenation kinetics were studied with thermogravimetry, X-ray photoelectron spectroscopy, and hydrogenation experiments. Catalyst reduction at a high temperature (400 °C) under hydrogen flow was favorable because of a more effective reduction of nickel oxides. Formaldehyde had a considerable retarding effect on the aldol hydrogenation:  the hydrogenation rate was low until all of the formaldehyde was hydrogenated to methanol. The hydrogenation rate of TME-aldol was found to be significantly lower than that of TMP-aldol at low temperatures and ...