A. Nilgün Akin

Structure/activity relationships in coprecipitated nickel-alumina catalysts using CO2 adsorption and methanation

Abstract A series of coprecipitated Ni/Al 2 O 3 catalysts containing 0–25 wt.−% Ni were examined for total surface area, total pore volume, metal surface area, CO 2 adsorption and CO 2 methanation activity in order to study the relation between metal content, structure and catalyst activity. Coprecipitated Ni/Al 2 O 3 catalysts are found to be efficient promoters for methanation. Methanation activity is dependent on the nickel content and the degree of CO 2 adsorption at the reaction considered. Although Al 2 O 3 does not exhibit methanation activity, it is found to be active for CO 2 adsorption. Reverse spillover increases methane production per unit nickel surface particularly for catalysts with low Ni loadings.

CO2 Fixation by hydrogenation over coprecipitated Co/Al2O3

CO2 fixation by hydrogenation over coprecipitated 36 wt.% Co/Al2O3 has been studied under a range of reaction conditions to clarify the effects of reaction variables and to determine the kinetics and mechanism of the reaction. A comparison of the results with those reported for CO hydrogenation on the same catalyst indicates that, although product distributions of CO2 and CO hydrogenation differ, the kinetics and mechanism are similar.

Development and characterization of Pt–SnO2/γ-Al2O3 catalysts

Abstract Effects of several preparation parameters on the physical properties and low-temperature CO oxidation activity of γ-Al 2 O 3 supported Pt–SnO 2 catalysts were examined. Results obtained with different Pt and SnO 2 loadings and ratios are compared on the basis of 1 wt % Pt /6 wt % SnO 2 /γ-Al 2 O 3 which corresponds to an optimum atomic Pt:Sn ratio of 1:8. A space time of 15 mg min / ml gives the highest activity with no catalyst deactivation. Catalytic activity is enhanced in reaction mixtures containing excess oxygen (CO/O 2 =1/2 or 1), while the stoichiometric feed ratio of CO/O 2 =2 leads to catalyst deactivation and lower activity. Kinetic data show that low-temperature CO oxidation over 1 wt % Pt /6 wt % SnO 2 /γ-Al 2 O 3 is best described by a model based on oxygen adsorption on SnO 2 followed by reverse-spillover from the oxide onto Pt sites and surface reaction occurring on Pt sites between chemisorbed CO and oxygen, with dissociative adsorption of oxygen as the rate-determining step.

Kinetics of CO hydrogenation over coprecipitated cobalt-alumina

The kinetics of CO hydrogenation over coprecipitated 36 wt% Co/Al 2 O 3 was studied in a fixed-bed microreactor at atmospheric pressure. Intrinsic kinetic data were obtained in the initial rate region using four different CO concentrations and two different H 2 /CO ratios over the 473-523 K temperature range. The surface carbide mechanism with dissociative adsorption of hydrogen as the rate controlling step gives the most plausible kinetic model among the eight different models tested. C 1 -C 4 production rates are found to be strongly influenced by temperature, and optimum C 1 -C 4 hydrocarbon selectivity is obtained at 508 K. The activation energy for CO consumption and CH 4 formation are calculated as 74±2 kJ/mol and 84±2 kJ/mol, respectively.

The Effect of Preparation Variables on the CO Hydrogenation Activity of Coprecipitated Co/Al2O3 Catalysts

Studies have been conducted on the effect of preparation variables on the activity of coprecipitated cobalt-alumina catalysts to be used for the production of C 1 -C 4 hydrocarbons by CO hydrogenation. The preparation parameters considered were the precipitation pH, the precipitation agent, the metal loading, the reduction temperature and the reduction period. It was found that changing pH precipitation with a constant final pH between 11.0 and 12.5 and the use of NaOH together with nitrates as precursors yielded better catalysts with maximal metal surface area. The optimum cobalt loading for the selective production of C 1 -C 4 hydrocarbons is around 35 wt%. Optimum activity and selectivity are obtained by applying an 8-h reduction scheme at 648 K under 100 cm 3 /min hydrogen. Calcination prior to reduction has a detrimental effect on metal surface area and hence on catalytic activity.

CO Hydrogenation by K-Promoted Coprecipitated Co/Al2O3

Effect of K promotion on the CO hydrogenation activity and selectivity of coprecipitated Co/Al2O3 has been studied. K addition is found to lower total activity while enhancing C2-C4 olefins selectivity; kinetic data indicate that the reaction mechanism is not affected.

Adsorption and reaction studies on cobalt/alumina catalysts prepared by changing pH coprecipitation

Co/Al2O3 catalysts prepared by changing pH coprecipitation with Co loadings in the 8.7–36 wt.% range were analyzed by TSA, TPV, pore structure, XRD as well as CO, H2, O2 adsorption and CO hydrogenation. High O2 uptake and reducibility coupled with low dispersion and constant MSA above 17 wt.% Co indicate large crystallites that are less exposed to H2. CO hydrogenation per Co site decreases with increasing dispersion or decreasing metal loading.