Periodic Reporting for period 2 - MECHANISM (The effect of water on the Fischer-Tropsch reaction mechanism and kinetics over bimetallic Co-based catalysts: Theoretical and experimental studies)
Période du rapport: 2019-04-03 au 2020-04-02
The Fischer-Tropsch Synthesis (FTS) is currently an industrial catalytic reaction that converts a gas mixture of carbon monoxide and hydrogen (syngas) into liquid hydrocarbons (synthetic fuels) and water. The FTS reaction provides the most economic path for the synthesis of liquid fuels free of sulphur and with lower soot emissions than conventional fuels produced in the oil refineries. H2O is formed during the FTS and influences rates and selectivities of reaction products. This project addresses the roles of void structure, Co nanoparticle size, extent of reduction of Co oxide precursors and experimental conditions (reaction temperature, total pressure of reactants and time on stream) on the magnitude of these rate and selectivity enhancements by the presence of water (added on purpose or increases in concentration with increasing residence time).
This project has six objectives: (1) the training and career development of the researcher; (2) the synthesis of bimetallic Co-based catalysts of uniform composition and a range of mean cluster diameter; (3) the physicochemical characterization of bimetallic Co-based catalytic materials, using TEM, PXRD, BET and TPD; (4) the understanding of the influence of water on the catalytic behaviour of these catalytic materials; (5) the elucidation of mechanistic details using DFT calculations, SSITKA-DRIFTS and -MS technique and transient experiment in order to study the effect of water, support structure and cluster size on the nature and reactivity of reaction intermediates; (6) the dissemination of results and public engagements.
This project has six objectives: (1) the training and career development of the researcher; (2) the synthesis of bimetallic Co-based catalysts of uniform composition and a range of mean cluster diameter; (3) the physicochemical characterization of bimetallic Co-based catalytic materials, using TEM, PXRD, BET and TPD; (4) the understanding of the influence of water on the catalytic behaviour of these catalytic materials; (5) the elucidation of mechanistic details using DFT calculations, SSITKA-DRIFTS and -MS technique and transient experiment in order to study the effect of water, support structure and cluster size on the nature and reactivity of reaction intermediates; (6) the dissemination of results and public engagements.
Cobalt-based catalysts (M1–M2/support) were prepared by the incipient wetness impregnation method, with different pore size of support (3.3-11.6 nm), Co loading (10-30 wt%), noble metal loading (0.5-1 wt%) and support (SiO2, γ-Al2O3 and La2O3-γ-Αl2O3). The Co-based catalysts were characterized by TEM, PXRD, BET, H2-chemisorption, O2-titration, H2-TPR, TIR, TPD-H2, TPD-CO techniques. The catalysts were tested towards FTS reaction with H2O present in the synthesis gas feed stream. The effect of: (i) void structure, (ii) Co nanoparticle size, (iii) extent of reduction of Co precursors and (iv) experimental conditions (reaction temperature, total pressure of reactants and time on stream) were investigated. It was found that the pore size of support and the experimental conditions plays an important role on the effect of water on the FTS rates. SSITKA-MS, -DRIFTS and TIH/TPH experiments were used for the evaluation of surface concentration and chemical structure of active and inactive intermediate species. The main reason of catalyst deactivation was the accumulation of inactive -CxHy with time on stream (TOS) that may affect the binding strength of co-adsorb active intermediates or may occupy sites where active species can formed.
The MECHANISM project results were presented to society by participation in the European Researcher’s Night, thought a video, an article in local magazines, a website (http://www.mechanism.ucy.ac.cy) and a lecture to undergraduate students (Marie Curie Ambassador). In addition, the results were presented to the scientific community thought six (6) scientific publications in peer-reviewed international scientific journals of high impact factor, one (1) presentation in international conference and five (5) presentations in the department.
The MECHANISM project results were presented to society by participation in the European Researcher’s Night, thought a video, an article in local magazines, a website (http://www.mechanism.ucy.ac.cy) and a lecture to undergraduate students (Marie Curie Ambassador). In addition, the results were presented to the scientific community thought six (6) scientific publications in peer-reviewed international scientific journals of high impact factor, one (1) presentation in international conference and five (5) presentations in the department.
The pore size of support plays an important role on the effect of water on the FT rate. Catalysts with large pore size shows positive effect of water on the CO consumption rate, while catalysts with medium and small pore size shows negligible effect. These rate enhancements for large pore size catalysts cause by water are independent on the Co nanoparticle size and the extent of reduction of cobalt. Important role on the effect of water on CO consumption rate plays the reaction temperature and the total pressure of reactants. In all cases (small and large pore size), CH4 selectivity decreases and C5+ selectivity increases with increasing the water partial pressure.
H2O does not significantly affect the concentration and chemical structure on active and inactive species (SSITKA-MS, -DRIFTS, TIH/TPH). The surface coverage of inactive species are constant with Co nanoparticle size and increased with increasing time on stream (TOS). The surface coverage of active CO-s and CHx-s increased with Co nanoparticle size. On the contrary, the surface coverage of active CO-s stayed practically constant and that of CHx-s decreased with increasing TOS. The main reason of catalyst deactivation was the accumulation of inactive -CxHy with TOS that may affect the binding strength of co-adsorb active intermediates or may occupy sites where active species can formed. The D-KIE estimated by a novel 13CO/D2-SSITKA experiment and gave an inverse D-KIE for CO consumption and CH4 formation, independent of dCO.
This project is important from an economic point of view since the price of crude oil is rising frequently (production of synthetic fuels) and the development of more active and selective FTS catalysts would offer an alternative given the environmental advantages of fuels derived from FTS. The results of this project are considered very important and strongly linked to the European energy needs.
H2O does not significantly affect the concentration and chemical structure on active and inactive species (SSITKA-MS, -DRIFTS, TIH/TPH). The surface coverage of inactive species are constant with Co nanoparticle size and increased with increasing time on stream (TOS). The surface coverage of active CO-s and CHx-s increased with Co nanoparticle size. On the contrary, the surface coverage of active CO-s stayed practically constant and that of CHx-s decreased with increasing TOS. The main reason of catalyst deactivation was the accumulation of inactive -CxHy with TOS that may affect the binding strength of co-adsorb active intermediates or may occupy sites where active species can formed. The D-KIE estimated by a novel 13CO/D2-SSITKA experiment and gave an inverse D-KIE for CO consumption and CH4 formation, independent of dCO.
This project is important from an economic point of view since the price of crude oil is rising frequently (production of synthetic fuels) and the development of more active and selective FTS catalysts would offer an alternative given the environmental advantages of fuels derived from FTS. The results of this project are considered very important and strongly linked to the European energy needs.