Browsing by Author "Yildiz, Fikret"

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A Comprehensive Study of Hydrogen Production From Ammonia Borane Via Pdcoag/Ac Nanoparticles and Anodic Current in Alkaline Medium: Experimental Design With Response Surface Methodology
(Higher Education Press, 2020) Celik Kazici, Hilal; Yilmaz, Sakir; Sahan, Tekin; Yildiz, Fikret; Er, Omer Faruk; Kivrak, Hilal
In this paper, the optimization of hydrogen (H-2) production by ammonia borane (NH3BH3) over PdCoAg/AC was investigated using the response surface methodology. Besides, the electro-oxidation of NH3BH3 was determined and optimized using the same method to measure its potential use in the direct ammonium boran fuel cells. Moreover, the ternary alloyed catalyst was synthesized using the chemical reduction method. The synergistic effect between Pd, Co and Ag plays an important role in enhancement of NH3BH3 hydrolysis. In addition, the support effect could also efficiently improve the catalytic performance. Furthermore, the effects of NH3BH3 concentration (0.1-50 mmol/5 mL), catalyst amount (1-30 mg) and temperature (20 degrees C-50 degrees C) on the rate of H-2 production and the effects of temperature (20 degrees C-50 degrees C), NH3BH3 concentration (0.05-1 mol/L) and catalyst amount (0.5-5 mu L) on the electro-oxidation reaction of NH3BH3 were investigated using the central composite design experimental design. The implementation of the response surface methodology resulted in the formulation of four models out of which the quadratic model was adjudged to efficiently appropriate the experimental data. A further statistical analysis of the quadratic model demonstrated the significance of the model with a p-value far less than 0.05 for each model and coefficient of determination (R-2) of 0.85 and 0.95 for H-2 production rate and NH3BH3 electrroxidation peak current, respectively.
Novel Activated Carbon Supported Trimetallic Pdcoag Nanoparticles as Efficient Catalysts for the Hydrolytic Dehydrogenation of Ammonia Borane
(Pergamon-elsevier Science Ltd, 2019) Kazici, Hilal Celik; Yildiz, Fikret; Izgi, Mehmet Sait; Ulas, Berdan; Kivrak, Hilal
Activated carbon (AC) supported palladium, cobalt and silver nanoparticle (PdCoAg/AC) catalysts were prepared by in situ reduction of sodium borohydride (NaBH4) and characterized by various techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX), Transmission electron microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). The PdCoAg/AC catalyst is active in the hydrolysis of ammonia-borane (AB) even at low temperatures. Compared with mono- (Pd) and bi-metallic (PdCo) nanoparticles, this trimetallic (PdCoAg) structure showed greatly increased catalytic activity for AB hydrolysis. Their hydrolysis completion time was 50 s. This study also included full experimental details of kinetic data to determine the activation parameters (Ea, Delta H and Delta S) for the rate law and the catalytic hydrolysis of AB. In addition, the PdCoAg/AC catalysts had favorable catalytic activity also after seven runs. Hydrogen generation rate (HG), Ea, Delta H and Delta S were obtained at 25 degrees C as 4666.66 mL min(-1)g(-1) (2 mmol AB and 50 mg PdCoAg/AC), 26.836 kJ mol(-1), 29.416 kJ mol(-1) and -108.42 J mol(-1)K(-1), respectively. In addition, the study showed that Pd0.6Co0.2CAg0.2/AC (Pd:Co:Ag atomic ratio = 6:2:2) showed the total turnover frequency (TOF) value of 6624 h(-1). These results demonstrate that the PdCoAg/AC catalyst is a promising alternative in search of the practical application of AB as a hydrogen storage material for fuel cell applications. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.