Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 4Citation - Scopus: 3Atomic-Scale Insights Into Carbon Dioxide Hydrogenation Over Bimetallic Iron-Cobalt Catalysts: a Density Functional Theory Study(MDPI, 2023) Tuncer, Dilan; Kızılkaya, Ali CanThe conversion of carbon dioxide to fuels and chemicals is a promising long-term approach for mitigating CO2 emissions. Despite extensive experimental efforts, a fundamental understanding of the bimetallic catalytic structures that selectively produce the desired products is still lacking. Here, we report on a computational surface science approach into the effect of the Fe doping of Co(111) surfaces in relation to CO2 hydrogenation to C1 products. Our results indicate that Fe doping increases the binding strength of surface species but slightly decreases the overall catalytic activity due to an increase in the rate-limiting step of CO dissociation. FeCo(111) surfaces hinder hydrogenation reactions due to lower H coverages and higher activation energies. These effects are linked to the Lewis basic character of the Fe atoms in FeCo(111), leading to an increased charge on the adsorbates. The main effect of Fe doping is identified as the inhibition of oxygen removal from cobalt surfaces, which can be expected to lead to the formation of oxidic phases on bimetallic FeCo catalysts. Overall, our study provides comprehensive mechanistic insights related to the effect of Fe doping on the catalytic behavior and structural evolution of FeCo bimetallic catalysts, which can contribute to the rational design of bimetallic catalysts.Article Citation - WoS: 21Citation - Scopus: 21A Promising Catalyst for the Dehydrogenation of Perhydro-Dibenzyltoluene: Pt/Al2 O3 Prepared by Supercritical Co2 Deposition(MDPI, 2022) Modisha, Phillimon; Garidzirai, Rudaviro; Güneş, Hande; Bozbağ, Selmi Erim; Rommel, Sarshad; Uzunlar, Erdal; Aindow, Mark; Erkey, Can; Bessarabov, DmitriPt/Al2 O3 catalysts prepared via supercritical deposition (SCD), with supercritical CO2, wet impregnation (WI) methods and a selected benchmark catalyst, were evaluated for the dehydrogenation of perhydro-dibenzyltoluene (H18-DBT) at 300◦ C in a batch reactor. After ten dehydrogenation runs, the average performance of the catalyst prepared using SCD was the highest compared to the benchmark and WI-prepared catalysts. The pre-treatment of the catalysts with the product (dibenzyltoluene) indicated that the deactivation observed is mainly due to the adsorbed H0-DBT blocking the active sites for the reactant (H18-DBT). Furthermore, the SCD method afforded a catalyst with a higher dispersion of smaller sized Pt particles, thus improving catalytic performance towards the dehydrogenation of H18-DBT. The particle diameters of the SCD-and WI-prepared catalysts varied in the ranges of 0.6–2.2 nm and 0.8–3.4 nm and had average particle sizes of 1.1 nm and 1.7 nm, respectively. Energy dispersive X-ray spectroscopy analysis of the catalysts after ten dehydrogenation runs revealed the presence of carbon. In this study, improved catalyst performance led to the production of more liquid-based by-products and carbon material compared to catalysts with low catalytic performance.Article Citation - WoS: 6Citation - Scopus: 9Mechanistic Insights Into the Effect of Sulfur on the Selectivity of Cobalt-Catalyzed Fischer–tropsch Synthesis: a Dft Study(MDPI, 2022) Dağa, Yağmur; Kızılkaya, Ali CanSulfur is a common poison for cobalt-catalyzed Fischer–Tropsch Synthesis (FTS). Alt-hough its effects on catalytic activity are well documented, its effects on selectivity are controversial. Here, we investigated the effects of sulfur-covered cobalt surfaces on the selectivity of FTS using density functional theory (DFT) calculations. Our results indicated that sulfur on the surface of Co(111) resulted in a significant decrease in the adsorption energies of CO, HCO and acetylene, while the binding of H and CH species were not significantly affected. These findings indicate that sulfur increased the surface H/CO coverage ratio while inhibiting the adsorption of carbon chains. The elementary reactions of H-assisted CO dissociation, carbon and oxygen hydrogenation and CH coupling were also investigated on both clean and sulfur-covered Co(111). The results indicated that sulfur decreased the activation barriers for carbon and oxygen hydrogenation, while increasing the barriers for CO dissociation and CH coupling. Combining the results on elementary reactions with the modification of adsorption energies, we concluded that the intrinsic effect of sulfur on the selectivity of cobalt-catalyzed FTS is to increase the selectivity to methane and saturated short-chain hy-drocarbons, while decreasing the selectivity to olefins and long-chain hydrocarbons.Article Citation - WoS: 11Citation - Scopus: 12Numerical Modelling Assisted Design of a Compact Ultrafiltration (uf) Flat Sheet Membrane Module(MDPI, 2021) Bopape, Mokgadi F.; Van Geel, Tim; Dutta, Abhishek; Van der Bruggen, Bart; Onyango, Maurice StephenThe increasing adoption of ultra-low pressure (ULP) membrane systems for drinking water treatment in small rural communities is currently hindered by a limited number of studies on module design. Detailed knowledge on both intrinsic membrane transport properties and fluid hydrodynamics within the module is essential in understanding ULP performance prediction, mass transfer analysis for scaling-up between lab-scale and industrial scale research. In comparison to hollow fiber membranes, flat sheet membranes present certain advantages such as simple manufacture, sheet replacement for cleaning, moderate packing density and low to moderate energy usage. In the present case study, a numerical model using computational fluid dynamics (CFD) of a novel custom flat sheet membrane module has been designed in 3D to predict fluid flow conditions. The permeate flux through the membrane decreased with an increase in spacer curviness from 2.81 L/m(2)h for no (0%) curviness to 2.73 L/m(2)h for full (100%) curviness. A parametric analysis on configuration variables was carried out to determine the optimum design variables and no significant influence of spacer inflow or outflow thickness on the fluid flow were observed. The numerical model provides the necessary information on the role of geometrical and operating parameters for fabricating a module prototype where access to technical expertise is limited.