Browsing by Subject "Formic acid"

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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
Electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon
(Elsevier, 2017) Topuz, F.; Uyar, T.
The electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon was shown, and the detailed studies were conducted to correlate the fiber morphology with electrospinning process parameters and gelatin concentration in electrospinning solution. Particularly, variations in the applied voltage and the concentration of gelatin led to the transition of fiber shape from round to flat/ribbon. The formation of flat-shaped fibers was attributed to rapid evaporation of the solvent (formic acid) from the fiber matrix with increasing the applied voltage and gelatin concentration. On the other hand, round fibers were due to the steady evaporation of formic acid throughout the cross-section of fibers. WAXS analysis revealed that the loss of triple-helical crystalline structure in gelatin after the electrospinning process. The gelatin fibers were cross-linked through treatment with toluene 2,4-diisocyanate (TDI) in a mixed solution of acetone and pyridine, and XPS confirmed the cross-linking of the fibers over an increased carbon content on the elemental composition of the fiber surface due to the incorporated TDI moieties. Overall, this study focuses on morphological tuning of gelatin electrospun fibers towards a flat/ribbon-like structure by variation of electrospinning parameters and polymer concentration, and thus, the proposed concept can be adapted towards flattened/ribbon-like fibers of other protein-based systems by electrospinning.
Open Access
MnOx-Promoted pdAg alloy nanoparticles for the additive-free dehydrogenation of formic acid at room temperature
(American Chemical Society, 2015) Bulut, A.; Yurderi, M.; Karatas, Y.; Say, Z.; Kivrak H.; Kaya, M.; Gulcan, M.; Ozensoy, E.; Zahmakiran, M.
Formic acid (HCOOH) has a great potential as a safe and a convenient hydrogen carrier for fuel cell applications. However, efficient and CO-free hydrogen production through the decomposition of formic acid at low temperatures (<363 K) in the absence of additives constitutes a major challenge. Herein, we present a new heterogeneous catalyst system composed of bimetallic PdAg alloy and MnOx nanoparticles supported on amine-grafted silica facilitating the liberation of hydrogen at room temperature through the dehydrogenation of formic acid in the absence of any additives with remarkable activity (330 mol H2·mol catalyst-1·h-1) and selectivity (>99%) at complete conversion (>99%). Moreover this new catalytic system enables facile catalyst recovery and very high stability against agglomeration, leaching, and CO poisoning. Through a comprehensive set of structural and functional characterization experiments, mechanistic origins of the unusually high catalytic activity, selectivity, and stability of this unique catalytic system are elucidated. Current heterogeneous catalytic architecture presents itself as an excellent contender for clean hydrogen production via room-temperature additive-free dehydrogenation of formic acid for on-board hydrogen fuel cell applications.