Lars-Eric Lindfors

Synthesis, characterization and application of H-MCM-22, Ga-MCM-22 and Zn-MCM-22 zeolite catalysts in the aromatization of n-butane

Abstract The H-MCM-22, Ga-MCM-22 and Zn-MCM-22 zeolite catalysts were synthesized and characterized by X-ray powder diffraction, scanning electron microscopy, X-ray fluorescence, energy dispersive X-ray analysis, temperature programmed desorption of ammonia and nitrogen adsorption. The study of the acidic properties of the synthesized zeolite catalysts revealed that the catalysts comprised of Bronsted and Lewis acid sites. n-Butane aromatization was investigated over the H-MCM-22, Ga-MCM-22 and Zn-MCM-22 zeolite catalysts. The effect of reaction temperature, weight hourly space velocity and time on stream on the conversion of n-butane and selectivity to aromatic hydrocarbons were studied over the synthesized catalysts. The type and nature of active sites in the aromatization of n-butane over the prepared MCM-22 catalysts have been examined. The reaction mechanism of n-butane conversion and the shape-selective property of the MCM-22 catalysts in light of their unique pore system with supercages are also discussed. The Ga- and Zn-modified MCM-22 zeolite catalysts exhibited high activity in the conversion of n-butane and selectivity to aromatic hydrocarbons. The aromatic hydrocarbons produced over these catalysts were benzene, toluene, ethyl benzene and isomers of xylene.

Catalytic combustion of propane and natural gas over Cu and Pd modified ZSM zeolite catalysts

Abstract Copper-exchanged ZSM-5, ZSM-11 and ZSM-48 as well as Pd-ZSM-5 zeolite catalysts were prepared and tested for their light-off and conversion behaviour in complete oxidation of propane and natural gas. Metal modified ZSM zeolite catalysts were found to be superior to the Pd and Cu/alumina catalysts prepared for comparison. Cu-ZSM-5 (Cu, 1.3 wt.-%) appeared to be the most active of the Cu-containing ZSM catalysts exhibiting combustion efficiencies of 97.6 and 94.8% for propane and natural gas, respectively. The method of introducing Pd into the zeolite was found to affect the catalysts activity strongly. Pd-ZSM-5 catalysts prepared by ion-exchange were more active than when the Pd was introduced into the zeolite during the process of hydrothermal zeolite synthesis. Combustion efficiencies of 100 and 98.1% for propane and natural gas combustion were achieved with Pd-ZSM-5 (Pd, 0.9 wt.-%) prepared by the ion-exchange method. The light-off temperatures were found to increase as: Pd-ZSM-5

Liquid-phase hydrogenation of citral over an immobile silica fibre catalyst

A new knitted silica fibre catalyst was introduced into liquid-phase hydrogenation of organic compounds. The fibre catalyst combines the advantages of catalyst slurries and large catalyst particles: diffusional limitations are suppressed and the catalyst is immobile. Nickel-impregnated silica fibres were used in the hydrogenation of citral to citronellal and citronellol in a tubular glass reactor where the catalyst was packed in two layers. The liquid phase was recirculated while the gas phase was flowing concurrently through the reactor to the vent. The highest selectivities to the desired product, citronellol, exceeded 90%. The catalyst performance was competitive with a conventional crushed nickel catalyst.

Enhancement of the catalytic activity of Cu-ZSM-5 for nitric oxide decomposition by introduction of copper during the zeolite synthesis

Abstract Decomposition of nitric oxide over different metal containing ZSM-5 catalysts was studied. The catalysts were prepared by ion-exchange, impregnation, metal introduction during synthesis and combinations of these methods. Introduction of copper during synthesis of the ZSM-5 catalyst combined with copper ion-exchange resulted in a catalyst, Cu(i)-Cu(s)-ZSM-5, which was more active than only copper ion-exchanged ZSM-5, Cu(i)-ZSM-5. Catalysts with Co, Ni or Ga introduced during synthesis combined with copper ion-exchange had about the same activity as Cu(i)-ZSM-5. Impregnation of the copper ion-exchanged ZSM-5 catalyst with Cu, Co, Ni or Ag, using the incipient wetness technique decreased the conversion. Temperature-programmed desorption studies of nitric oxide from pre-oxidized catalysts indicated a larger number of active sites for the Cu(i)-Cu(s)-ZSM-5 compared to Cu(i)-ZSM-5.

Synthesis and characterization of H-ZSM-22, Zn-H-ZSM-22 and Ga-H-ZSM-22 zeolite catalysts and their catalytic activity in the aromatization of n-butane

Abstract K-ZSM-22 zeolites with a Si/Al ratio of 53 have been synthesized by means of the hydrothermal synthesis method using 1,6-diaminohexane as the templating agent. The H-ZSM-22, Ga and Zn modified ZSM-22 zeolite catalysts have been prepared and characterised by X-ray powder diffraction (Philips pw 1830), scanning electron microscopy (Leica Cambridge Stereoscan 360), nitrogen adsorption (Carlo Erba Instruments), X-ray fluorescence (Outokumpu-8000) and temperature programmed desorption of ammonia. The synthesised ZSM-22 zeolite was highly crystalline and free of amorphous material. The TPD of ammonia profiles revealed that the H-ZSM-22, Ga and Zn modified ZSM-22 were acidic and consisted of Bronsted and Lewis acid sites. The catalytic activity were investigated for the conversion of n-butane to aromatic hydrocarbons over H-ZSM-22, Ga-H-ZSM-22 and Zn-H-ZSM-22 catalysts. Further, the effect of temperature and the space velocity on the conversion of n-butane and the selectivity to aromatic hydrocarbons were studied. The selectivity to aromatics was higher for Ga and Zn modified ZSM-22 than for H-ZSM-22. The effect of time on stream on n-butane conversion and the selectivity to aromatics was studied at 803 K for 4.5 h.

A review of the precipitation of nickel from salt solutions by hydrogen reduction

This review is a general presentation of principal phenomena, procedures, catalysts and problems involved in the hydrogen reduction of nickel salt solutions. This approach does not include a presentation of reduction rates as a function of temperature, pressure and addition agents, but more general hydrogen reduction basics and phenomena are discussed.

A dynamic study of the water-gas shift reaction over an industrial ferrochrome catalyst

Abstract The water-gas shift reaction over an industrial ferrochrome catalyst (ICI 15-4) was studied by transient experiments in a gradientless spinning basket reactor at 563–638 K and atmospheric pressure. The responses of CO, CO 2 , and H 2 were measured after step changes at the reactor inlet. The stationary kinetics were described with a first-order rate expression with respect to CO. The rate constants were determined at four temperatures. The CO 2 responses followed approximately a first-order behavior, whereas the dynamics of the H 2 liberation was always slower than the CO 2 evolution. Hydrogen formation was retarded by H 2 O pretreatment of the catalyst. Two characteristic values of the total oxygen transfer through the catalyst were determined from the CO 2 and H 2 responses, corresponding to the catalyst pretreatments with the reactive gases (CO and H 2 O) and with H 2 O. The transient responses were modeled with a reaction mechanism involving rapid water adsorption and slow CO interconversion and H 2 desorption steps. The kinetic parameters of the simplified dynamic model were determined by regression analysis. The shift reactor start-up and shut-down could be predicted by the dynamic model developed.

Catalytic Combustion of Propane and Natural Gas over Silica-Fibre Supported Catalysts

ABSTRACT Different knitted silica-fibre supported metal oxides (oxides of Co, Ni, Mn, Cr) and various combinations of them, platinum-activated cobalt and nickel oxide catalysts as well as noble metal (Pt, Pd) catalysts were prepared. The catalysts were tested for their activity in propane and natural gas combustion in a continuous flow tube reactor at temperature range of 423-823 K and GHSV of 23900 and 47800 h−1. High combustion efficiencies were obtained by the metal oxides and platinum activated metal oxides. Co3O4 was found to be the most active single metal oxide catalyst in propane combustion. The low temperature activity of metal oxide was strongly improved by use of platinum as an activator. The propane combustion over Pd/SiO2 was found to be structure sensitive under our experimental conditions. The dependence of the rate of propane combustion over noble metal containing catalysts was found to be zero order with respect to oxygen and one with respect to propane. The reaction orders over metal oxi...

Catalytic combustion of propane over Pt and Cu modified ZSM-5 zeolite catalysts

Abstract ZSM-5 zeolites were modified with copper and platinum by ion exchange and during the process of hydrothermal zeolite synthesis. The catalytic activity of the prepared Pt and Cu ZSM-5 zeolite catalysts was tested for complete oxidation of propane. It was observed that the mode of introduction of metals into the zeolite and the metal content influenced the catalytic activity. Copper introduced into the zeolite by ion exchange under basic conditions exhibited a high catalytic activity. Combustion efficiencies of 98.9 and 97.6% were achieved with the Cu ZSM-5 and Pt ZSM-5 catalysts containing 5.2 wt% Cu and 0.27 wt% Pt, respectively. The light-off temperature of the platinum containing catalyst was about 30 K lower than that of the 5.2 Cu ZSM-5 catalyst. The Cu ZSM-5 prepared during the process of hydrothermal synthesis exhibited a lower catalytic activity as compared to the ion exchanged Cu ZSM-5 catalysts. Temperature programmed desorption (TPD) measurements of CO and O2 were used to interpret the catalytic activity. The results indicated the important role of the extra lattice oxygen on these catalysts.

Modelling of the high temperature water gas shift reaction with stationary and transient experiments

Abstract The kinetics of the water gas shift reaction over the industrial ferrochrome catalyst ICI 15-4 was investigated with stationary and transient experiments in a gradientless reactor at the temperatures 290°C–365°C. The steady state reaction rate data showed that the reaction is of first order with respect to CO and of low order with respect to H2O. At the higher temperatures (350°C, 365°C) the reaction becomes pore diffusion limited. The activation energy of the reaction measured at the lower temperatures (290°C, 319°C) is about 122 kJ/mol. Transient experiments showed that H2 was always liberated slower than CO2 at the reactor start-up. Pretreatment of the catalyst with H2O had a retarding effect on the formation of H2, whereas the formation of CO2 was independent of the H2O-pretreatment. The same tendencies in the step responses were detected throughout the whole temperature and concentration domain investigated. The step response experiments enabled an elucidation of the reaction mechanism. Several mechanisms proposed in the literature were discussed and a new mechanism including two different types of active sites and both adsorptive and regenerative reaction steps was proposed.