Browsing by Author "Karakurt, Bartu"

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Open Access
Core-crown quantum nanoplatelets with favorable type-II heterojunctions boost charge separation and photocatalytic NO oxidation on TiO2
(Wiley, 2020-09) Ebrahimi, Elnaz; İrfan, Muhammad; Shabani, Farzan; Koçak, Yusuf; Karakurt, Bartu; Erdem, E.; Demir, Hilmi Volkan; Özensoy, Emrah
Functionalization of TiO2 (P25) with oleic acid‐capped CdSe(core)/CdSeTe(crown) quantum‐well nanoplatelets (NPL) yielded remarkable activity and selectivity toward nitrate formation in photocatalytic NOx oxidation and storage (PHONOS) under both ultraviolet (UV‐A) and visible (VIS) light irradiation. In the NPL/P25 photocatalytic system, photocatalytic active sites responsible for the NO(g) photo‐oxidation and NO2 formation reside mostly on titania, while the main function of the NPL is associated with the photocatalytic conversion of the generated NO2 into the adsorbed NO3− species, significantly boosting selectivity toward NOx storage. Photocatalytic improvement in NOx oxidation and storage upon NPL functionalization of titania can also be associated with enhanced electron‐hole separation due to a favorable Type‐II heterojunction formation and photo‐induced electron transfer from the CdSeTe crown to the CdSe core of the quantum well system, where the trapped electrons in the CdSe core can later be transferred to titania. Re‐usability of NPL/P25 system was also demonstrated upon prolonged use of the photocatalyst, where NPL/P25 catalyst surpassed P25 benchmark in all tests.
Open Access
Effects of Bronsted and Lewis bases on formic acid dehydrogenation selectivity of Pd(111) single crystal model catalyst
(2020-06) Karakurt, Bartu
Formic acid (FA) is an environmentally friendly hydrogen-based energy vector that can be obtained from renewable biomass feedstocks. However, catalytic decomposition of FA involves two different competing chemical pathways called dehydration and dehydrogenation. Thus, molecular level studies focusing on the selective catalytic FA dehydrogenation are essential for establishing structure-reactivity relationships which can be used in order to increase the catalytic dehydrogenation selectivity. In the current work, effects of Bronsted and Lewis bases on catalytic FA dehydrogenation selectivity were studied under ultra-high vacuum (UHV) conditions on an atomically well-defined Pd(111) single crystal model catalyst surface by using temperature programmed desorption/temperature programmed reaction spectroscopy (TPD/TPRS), X-Ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) techniques. Doubly-deuterated FA (DCOOD) was used as the FA source, while ammonia and manganese oxide were chosen as the model Bronsted and Lewis bases. Adsorption and subsequent surface decomposition reaction of DCOOD on Pd(111) showed that model catalyst was not totally selective towards dehydrogenation. Functionalizing the Pd(111) surface with ammonia suppressed the FA dehydration and boosted the dehydrogenation pathway, where positive influence of ammonia on FA dehydrogenation selectivity decayed when ammonia coverage was greater than 1 ML. A boost in hydrogen generation was observed in the catalytic FA dehydrogenation on manganese oxide-deposited Pd(111) surface (at sub-monolayer manganese oxide regime) as compared to that of a clean Pd(111) model catalyst. It was found out that manganese oxide can enhance FA dehydrogenation by acting as a promoter and/or catalytically contributing to the reaction depending on the oxidation state composition.
Open Access
Enhancement of formic acid dehydrogenation selectivity of Pd(111) single crystal model catalyst surface via Brønsted bases
(American Chemical Society, 2019) Karakurt, Bartu; Koçak, Yusuf; Özensoy, Emrah
The influence of ammonia (NH3) on the doubly deuterated formic acid (DCOOD, FA) dehydrogenation selectivity for a Pd(111) single crystal model catalyst surface was investigated under ultrahigh vacuum conditions using temperature-programmed desorption and temperature-programmed reaction spectroscopy techniques. NH3 adsorption on Pd(111) revealed reversible, molecular desorption without any significant decomposition products, while DCOOD adsorption on Pd(111) yielded D2, D2O, CO, and CO2 as a result of dehydration and dehydrogenation pathways. Functionalizing the Pd(111) surface with ammonia suppressed the FA dehydration and enhanced the dehydrogenation pathway. The boost in the FA dehydrogenation of Pd(111) in the presence of NH3 can be linked to the ease of FA deprotonation as well as the stabilization of the decomposition intermediate (i.e., formate) due to the presence of ammonium counterions on the surface. In addition, the presence of a H-bonded ammonia network on the Pd(111) surface increased the hydrogen atom mobility and decreased the activation energy for molecular hydrogen desorption. In the presence of NH3, catalytic FA decomposition on Pd(111) also yielded amidation reactions, which further suppressed CO liberation and prevented poisoning of the Pd(111) active sites due to strongly bound CO species.
Open Access
Interaction of CO2 with MnOx/Pd(111) reverse model catalytic interfaces
(Wiley, 2023-07-03) Anıl, Arca; Sadak, Ömer Faruk; Karakurt, Bartu; Koçak, Yusuf; Lyubinetsky, Igor; Özensoy, Emrah
Understanding the activation of CO2 on the surface of the heterogeneous catalysts comprised of metal/metal oxide interfaces is of critical importance since it is not only a prerequisite for converting CO2 to value-added chemicals but also often, a rate-limiting step. In this context, our current work focuses on the interaction of CO2 with heterogeneous bi-component model catalysts consisting of small MnOx clusters supported on the Pd(111) single crystal surface. These metal oxide-on-metal ‘reverse’ model catalyst architectures were investigated via temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) techniques under ultra-high vacuum (UHV) conditions. Enhancement of CO2 activation was observed upon decreasing the size of MnOx nanoclusters by lowering the preparation temperature of the catalyst down to 85 K. Neither pristine Pd(111) single crystal surface nor thick (multilayer) MnOx overlayers on Pd(111) were not capable of activating CO2, while CO2 activation was detected at sub-monolayer (∼0.7 ML) MnOx coverages on Pd(111), in correlation with the interfacial character of the active sites, involving both MnOx and adjacent Pd atoms. © 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.
Open Access
Significance of the Mn-Oxidation state in catalytic and noncatalytic promotional effects of MnOx domains in formic acid dehydrogenation on Pd/MnOx interfaces
(American Chemical Society, 2020) Karakurt, Bartu; Koçak, Yusuf; Lyubinetsky, Igor; Özensoy, Emrah
The influence of MnOx overlayers/nanoclusters deposited on the Pd(111) single-crystal model catalyst surface on the catalytic dehydrogenation of double-deuterated formic acid (FA, DCOOD) was studied under ultrahigh vacuum conditions via temperature-programmed desorption and X-ray photoelectron spectroscopy techniques. A significant boost in D2 generation was observed in the catalytic FA dehydrogenation on MnOx/Pd(111) as compared to that of a clean Pd(111) model catalyst, demonstrating the cooperative interaction between Pd(111) and MnOx sites. Maximum FA conversion was observed at a submonolayer MnOx surface coverage of 0.25 ML (monolayer) on Pd(111), whereas D2 formation was found to be suppressed when the Pd(111) surface was entirely covered with relatively thick (15 ML) MnOx overlayers. A direct correlation between increasing relative abundance of oxidized Mn surface states (i.e., Mn2+, Mn3+, and Mn4+) and increasing catalytic FA dehydrogenation was observed. Different modes of promotion of FA dehydrogenation via MnOx (i.e., catalytic promotion versus noncatalytic/stoichiometric promotion) were discussed as a function of the differences in the model catalyst preparation and the extent of oxidation of the MnOx overlayer.
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Türk bisikleti ve Konya Şekerspor
(Bilkent University, 2016) Demirkaya, Ahmet; Karakurt, Bartu; Altınöz, Emir; Sürmeli, Damla; Saçkan, Koray