Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 13Citation - Scopus: 11Bottom-Up Synthesis of Platinum Dual-Atom Catalysts on Cerium Oxide(American Chemical Society, 2024) Mekkering, Martijn J.; Laan, Petrus C. M.; Troglia, Alessandro; Bliem, Roland; Kızılkaya, Ali Can; Rothenberg, Gadi; Yan, NingWe present here the synthesis and performance of dual-atom catalysts (DACs), analogous to well-known single-atom catalysts (SACs). DACs feature sites containing pairs of metal atoms and can outperform SACs due to their additional binding possibilities. Yet quantifying the improved catalytic activity in terms of proximity effects remains difficult, as it requires both high-resolution kinetic data and an understanding of the reaction pathways. Here, we use an automated bubble counter setup for comparing the catalytic performance of ceria-supported platinum SACs and DACs in ammonia borane hydrolysis. The catalysts were synthesized by wet impregnation and characterized using SEM, HAADF-STEM, XRD, XPS, and CO-DRIFTS. High-precision kinetic studies of ammonia borane hydrolysis in the presence of SACs show two temperature-dependent regions, with a transition point at 43 degrees C. Conversely, the DACs show only one regime. We show that this is because DACs preorganize both ammonia borane and water at the dual-atom active site. The additional proximal Pt atom improves the reaction rate 3-fold and enables faster reactions at lower temperatures. We suggest that the DACs enable the activation of the water-O-H bond as well as increase the hydrogen spillover effect due to the adjacent Pt site. Interestingly, using ammonia borane hydrolysis as a benchmark reaction gives further insight into hydrogen spillover mechanisms, above what is known from the CO oxidation studies.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: 6Citation - Scopus: 8Effect of the Combination of Organic Acid Solutions on Tinplate Corrosion(Elsevier, 2022) Yıldırım, Koray; Kızılkaya, Ali CanTinplate corrosion as a result of canned food is typically tested in industry by tinplate in synthetic media based on single organic acids. However, the combination of organic acids, which is present in applied conditions, is not previously investigated in terms of its effect on tinplate corrosion mechanism. In this manuscript, we combine structural characterization of tinplate surfaces with electrochemical measurements, to investigate the corrosion mechanism of tinplate under acetic acid-NaCl, citric acid-NaCl, and a combined acetic acid, citric acid and NaCl media. The results show that the combined acid media causes does not result in a pronounced formation of a protective passivation layer, in contrast to the single acid based media. Our findings demonstrate the combined effects of the organic acids in corrosive media has to be taken into account for tinplate corrosion, as they can alter the corrosion mechanism. Furthermore, we show that combination of organic acids can accelerate tinplate corrosion testing in packaging industry. Thus, our findings can contribute to the design of new aging media for tinplate corrosion testing.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: 69Citation - Scopus: 77Design of Cobalt Fischer-Tropsch Catalysts for the Combined Production of Liquid Fuels and Olefin Chemicals From Hydrogen-Rich Syngas(American Chemical Society, 2021) Jeske, Kai; Kızılkaya, Ali Can; Lopez-Luque, Ivan; Pfaender, Norbert; Bartsch, Mathias; Concepcion, Patricia; Prieto, GonzaloAdjusting hydrocarbon product distributions in the Fischer-Tropsch (FT) synthesis is of notable significance in the context of so-called X-to-liquids (XTL) technologies. While cobalt catalysts are selective to long-chain paraffin precursors for synthetic jet- and diesel-fuels, lighter (C10-) alkane condensates are less valuable for fuel production. Alternatively, iron carbide-based catalysts are suitable for the coproduction of paraffinic waxes alongside liquid (and gaseous) olefin chemicals; however, their activity for the water-gas-shift reaction (WGSR) is notoriously detrimental when hydrogen-rich syngas feeds, for example, derived from (unconventional) natural gas, are to be converted. Herein the roles of pore architecture and oxide promoters of Lewis basic character on CoRu/Al2O3 FT catalysts are systematically addressed, targeting the development of catalysts with unusually high selectivity to liquid olefins. Both alkali and lanthanide oxides lead to a decrease in turnover frequency. The latter, particularly PrOx, prove effective to boost the selectivity to liquid (C5-10) olefins without undesired WGSR activity. In situ CO-FTIR spectroscopy suggests a dual promotion via both electronic modification of surface Co sites and the inhibition of Lewis acidity on the support, which has direct implications for double-bond isomerization reactivity and thus the regioisomery of liquid olefin products. Density functional theory calculations ascribe oxide promotion to an enhanced competitive adsorption of molecular CO versus hydrogen and olefins on oxide-decorated cobalt surfaces, dampening (secondary) olefin hydrogenation, and suggest an exacerbated metal surface carbophilicity to underlie the undesired induction of WGSR activity by strongly electron-donating alkali oxide promoters. Enhanced pore molecular transport within a multimodal meso-macroporous architecture in combination with PrOx as promoter, at an optimal surface loading of 1 Prat nm(-2), results in an unconventional product distribution, reconciling benefits intrinsic to Co- and Fe-based FT catalysts, respectively. A chain-growth probability of 0.75, and thus >70 C% selectivity to C5+ products, is achieved alongside lighter hydrocarbon (C5-10) condensates that are significantly enriched in added-value chemicals (67 C%), predominantly alpha-olefins but also linear alcohols, remarkably with essentially no CO2 side-production (<1%). Such unusual product distributions, integrating precursors for synthetic fuels and liquid platform chemicals, might be desired to diversify the scope and improve the economics of small-scale gas- and biomass-to-liquid processes.Article Citation - WoS: 13Citation - Scopus: 13Application of Work Function Measurements in the Study of Surface Catalyzed Reactions on Rh(1 0 0)(Taylor & Francis, 2018) Çağlar, Başar; Kızılkaya, Ali Can; Niemantsverdriet, J. W. (Hans); Weststrated, C. J. (Kees-Jan)The present article aims to show how work function measurements (WF) can be applied in the study of elementary surface reaction steps on metallic single crystal surfaces. The work function itself can in many cases not be interpreted directly, as it lacks direct information on structural and chemical nature of the surface and adsorbates, but it can be a powerful tool when used together with other surface science techniques which provide information on the chemical nature of the adsorbed species. We here, illustrate the usefulness of work function measurements using Rh(100) as our model catalyst. The examples presented include work function measurements during adsorption, surface reaction, and desorption of a variety of molecules relevant for heterogeneous catalysis. Surface coverage of adsorbates, isosteric heat of adsorption, and kinetic parameters for desorption, desorption/decomposition temperatures of surface species, different reaction regimes were determined by WF with the aid of other surface science techniques.Article Citation - WoS: 6Citation - Scopus: 6Effect of Ammonia on Cobalt Fischer-Tropsch Synthesis Catalysts: a Surface Science Approach(Royal Society of Chemistry, 2019) Kızılkaya, Ali Can; Niemantsverdriet, J. W.; Weststrate, C. J.Ammonia adsorption and decomposition on defect-rich hcp-Co(0001) surfaces were investigated under ultra-high vacuum conditions in order to provide a fundamental explanation for industrially observed ammonia poisoning of cobalt based Fischer-Tropsch synthesis (FTS) catalysts. Temperature-programmed desorption, infrared spectroscopy and work function measurements indicate that undercoordinated sites bind ammonia stronger than sites on flat Co(0001), and they also induce its dehydrogenation. Density functional theory calculations were employed to explore the reactivity of defective Co surfaces using the fcc-Co(211) as a model. The results indicate that the decomposition products (NH x ) adsorb strongly on or around the step site on fcc-Co(211). We find that NH (+2H ad ), adsorbed in the threefold site on the upper terrace, is equally stable as NH 2 (+H ad ), adsorbed in the bridge position at the step edge, both being significantly more stable than the equivalent species adsorbed on the flat Co(0001). The calculated activation barriers for NH 3,ad dehydrogenation steps are in reasonable agreement with the barriers obtained by fitting experimental data. Based on these fundamental insights, poisoning of cobalt nanoparticles during FTS by NH 3 contaminants can be linked mainly to the blocking of undercoordinated sites by strongly adsorbed NH 2 species.