Banca de DEFESA: RANDALL FERNANDO YEPEZ AYALA
Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.STUDENT : RANDALL FERNANDO YEPEZ AYALA
DATE: 24/02/2022
TIME: 14:00
LOCAL: https://meet.google.com/qxn-jfpz-qiy
TITLE:
Development of Co-Ce/HDL catalyst for hydrogen production from sodium borohydride hydrolysis
KEY WORDS:
hydrogen, sodium borohydride, catalyst, lamellar double hydroxide, catalytic doping, energy.
PAGES: 69
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Físico-Química
SUMMARY:
Currently, hydrogen (H2) is a promising alternative to non-fossil fuels, due to its good energy properties. Being a gaseous substance with defined physicochemical properties, its storage and transport become difficult. Therefore, the use of metal hydride complexes is a good option due to its ease of generating H2, in this case sodium borohydride (NaBH4) is one of the most studied and promising metal hydrides due to its high H2 storage capacity (10, 8% by weight), stability in alkaline solution at room temperature and safety in operational uses, in addition, the NaBH4 hydrolysis reaction generates the hydrogen product (H2) and the sodium metaborate by-product (NaBO2), which are not contaminants. Additionally, the generation of H2 can be more efficient when using catalysts such as: homogeneous catalysts, acid and metal complexes or heterogeneous catalysts, including metal-based and metal-free catalysts. The most viable catalyst for this dehydrogenation process is Double Lamellar Hydroxide (DLH), as it is highly stable in alkaline solutions, easy to produce and low cost, and can also be used as a support for catalysts. Therefore, this study aimed to evaluate the efficiency of an DLH and DLH doped with cobalt and cerium as a catalyst for the hydrolysis reaction of sodium borohydride to generate hydrogen. In this study, DLH from Mg/Al was synthesized and doped with cobalt (Co) and cerium (Ce) through the co-precipitation method with Mg/Al = 2 and Co/Ce = 3.25 ratios. The efficiency of the Co-Ce/DLH catalyst was evaluated by the volume of pure H2 generated, measured through the volume of water displaced from an inverted beaker filled with water, evaluating the effects of the 4 variables: concentration of NaBH4, dosage of the catalyst Co- Ce/DLH, NaOH concentration and reaction temperature. For this, a solution of NaBH4 and NaOH was prepared, at the concentrations mentioned above, for a volume of 20 mL of deionized water, using Co-Ce/DLH as a catalyst. As soon as the reaction started, the volume of hydrogen generated was determined as a function of time, with the final volume being 100 mL. The catalysts were characterized by: Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The shortest catalytic reaction time obtained was 3.25 minutes and the highest H2 generation rate was 52.54 mL/min for a concentration of 0.198 M NaBH4 and 0.94 M NaOH using 0.1 g of Co -Ce/DLH. The reaction order was zero for the range of NaBH4 concentration (0.066M – 0.198M), therefore, it will not depend on the amount of NaBH4, since for each iteration the final catalytic times are similar, which means they are close and the reaction became faster when Co-Ce/DLH and NaOH were added, affecting only reaction times. The activation energy was 34.44 kJ/mol, a low value which confirms that the reaction is temperature sensitive, but for values above 52.05 kJ/mol reported in previous works it is considered a high value, therefore the reaction needs more energy to take place and the main assumption is that the reaction is not temperature sensitive. The reaction mechanism follows the Langmuir-Hinshelwood model which takes place on the surface of the catalyst. The reuse of the catalyst showed good stability and catalytic activity within the 7 cycles studied. The characterizations of the catalysts showed the differences of HDL and Co-Ce/DLH, thus confirming that by adding the metals Co and Ce after the synthesis of HDL, the catalytic doping was successful, achieving the desired structure and chemical composition. Therefore, NaBH4 is a good H2 storage material, because even at minimal NaBH4 concentrations, high H2 generation rates were obtained and, additionally, the Co-Ce/DLH catalyst showed good catalytic results in the production of pure H2. These results indicate that the material studied (Co-Ce/DLH) is promising to generate H2 to feed a PEM-type fuel cell, in order to generate low-scale energy for electronic devices.
BANKING MEMBERS:
Presidente - 1314677 - CARMEM LUCIA DE PAIVA E SILVA ZANTA
Externo ao Programa - 3252578 - JOSÉ LEANDRO DA SILVA DUARTE
Interno - 2343745 - JULIO COSME SANTOS DA SILVA
Externa à Instituição - Suely Souza Leal de Castro - UERN
Interno - 1609640 - VINICIUS DEL COLLE