Emmanuel Iro

Novel Ni/SBA-15 catalysts were synthesised and their activity in the dry reforming of methane process was assessed. Extrudates, in the shape of pellets, of these materials were prepared and tested in a pyrolysis pilot plant fitted with a catalytic reactor for the sewage sludge pyrolysis tar removal. The Ni/SBA-15 catalyst pellets remained highly active and stable throughout the test duration, converting 100% tar in the hot gas to smaller non-condensable gases, thereby increasing the pyrolysis gas fraction and eliminating the problematic tar in the vapour stream. Catalyst characterisation with Scanning Electron Microscope (SEM), Energy Dispersive X-ray (EDX) analysis, Transmission Electron Microscope (TEM) and Thermogravimetric Analysis (TGA) confirmed that both, the Ni/SBA-15 powered catalyst and the pellets as well, were resistant to sintering and carbon deposition and remained highly active even with relatively high-level sulphur in the feed stream. The Ni/SBA-15 catalyst extrudates were prepared by mixing the powdered catalyst with varied amounts of colloidal silica binder and fixed amounts of methyl cellulose and water. The highest mechanical strength of the extrudates was determined to be for those obtained with 36% of the inorganic binder. The physical properties and catalytic activity of Ni/SBA-15 pellets with 36% colloidal silica was compared with the original powdered Ni/SBA-15 catalyst after crushing some of the pellets to powder to determine any binder inhibitory effect. The results confirm that colloidal silica binder did not inhibit the desired catalyst properties and performance in the reaction. Instead, an enhanced catalytic performance was observed.

Gold catalysts, with different particle sizes ranging from 19 to 556 Å, and supported on SBA-15 mesoporous silica, were prepared by using deposition-precipitation, co-precipitation, and impregnation methods. All samples were characterised by TEM, EXAFS, XPS, XRD, CFR (Continuous Flow Reactor), and TPR. The sample which proved to have the highest activity was characterised by TAP (Temporal Analysis of Products) as well. XPS, wide-angle XRD, EXAFS, and H₂-TPR measurements and data analysis confirmed that gold was present as Au⁰ only on all samples. The size of the Au nanoparticle was determined from TEM measurements and confirmed through wide-angle XRD measurements. EXAFS measurements showed that as the Au-Au coordination number decreased the Au-Au bond length decreased. TEM data analysis revealed a dispersion range from 58% (for the smallest particle size) to 2% (for the highest particle size). For Au particles’ sized lower that 60 Å, the Au dispersion was determined using a literature correlation between the dispersion and EXAFS Au-Au coordination number, and was in good agreement with the dispersion data obtained from TEM. The Au dispersion decreased as the particle size increased. CFR experiments validated the relationship between the size of the gold particles in a sample and the sample’s catalytic activity towards acetone oxidation. The lowest temperature for the acetone 100% conversion, i.e., 250 °C, was observed over the reduced catalyst sample with the smallest particle size. This sample not only showed the highest catalytic activity towards acetone conversion, but, at the same time, showed high reaction stability, as catalyst lifetime tests, performed for 25 h in a CFR at 270 °C for the as-synthesised sample, and at 220 °C for the reduced sample, have confirmed. TAP (Temporal Analysis of Products) measurements and data analysis confirmed a weak competitive adsorption of acetone and oxygen over the Au/SBA-15 sample. Based on TAP data, a combination of Eley–Rideal and Langmuir–Hinshelwood mechanisms for acetone complete oxidation was proposed.

Based on previous Computational Fluid Dynamics (CFD) design results, an 11 channel microreactor of dimensions (0.5 mm × 0.5 mm × 100 mm) (width × depth × length) and optimal manifold geometry was fabricated, coated with a newly-developed Au/SBA-15 catalyst and then integrated in an experimental rig specifically built for this research. Propane (as model volatile organic compound) oxidation experiments were conducted at three different flow velocities, 12.5, 15.4 and 17.5 m/min, respectively, at six temperatures, 150, 200, 225, 250, 275, and 300 °C, respectively. The catalyst was prepared by one-pot sol-gel synthesis of SBA-15 with MPTMS (3-mercaptopropyl-trimethoxy-silane) before loading with HAuCl₄ gold precursor and then characterized by SEM/EDX, TEM and wide angle XRD. A novel catalyst coating technique was developed, using airbrush (0.3 nozzle) to spray a catalyst slurry into the microchannels that produced a thin, firm and uniform layer of Au/SBA-15 catalyst coating inside the microreactor. The experimental measurements revealed that propane conversion increased as the flow feed rates decreased and increased with increasing temperatures in the reactor. For the built microreactor and for the flows and temperatures set, the combustion of propane was possible with measurable conversions and reasonable reactor stability, the performance of the catalyst appeared to be central to the satisfactory operation of the reactor.