(450g) Microwave Assisted Hydrogen Production from Ammonia over Carbon Supported Materials

In this study, hydrogen production from ammonia was investigated in a focused microwave heated system and the results were compared with the corresponding results obtained in a conventionally heated tubular reactor.

While fossil fuels have been still used as a main energy resource, alternative energy sources have gained great attention due to the decrease in the fossil fuel reserves and the increase in the concentration of CO₂, which is emitted to the atmosphere due to the usage of fossil fuels. Utilization of hydrogen as an alternative energy source especially by means of fuel cell application increases steadily, due to its energy content and its clean fuel properties. Since, the purity of hydrogen is very important especially for PEM fuel cells, in this study ammonia has been selected as a raw material for hydrogen production since it has high hydrogen content and can be stored and distributed easily by means of conventional methods as well as COx free hydrogen can be produced by decomposition of ammonia.

Nowadays, microwave energy is used as an alternative heating method to enhance heterogeneous chemical reactions, especially for endothermic ones. Differently from conventional methods, such as electrical resistance furnace, direct conversion of electromagnetic energy into heat can be achieved through microwave system instead of heat transfer. Therefore a temperature distribution in radial direction within the catalytic bed is avoided in comparison to conventionally heated system.

In this study, microwave assisted ammonia decomposition reaction was carried out over transition metal incorporated carbon supported catalysts. Carbon materials were used due to its superior properties as microwave absorbers in the reaction medium. Catalysts were synthesized following the impregnation procedure at different metal loadings and they were characterized by different techniques, namely, TGA, TPR, XRD, nitrogen physisorption, ICP, HRTEM/EDX after calcination, reduction and reaction steps. When the performances of the synthesized catalysts were evaluated in the conventional system with a GHSV of 36,000 ml/hg_cat, negligible activity was observed below 500^oC. In the case of microwave system, conversion of ammonia was observed at temperatures as low as 300^oC. Moreover complete conversion was achieved over the synthesized catalysts at a reaction temperature between 400-500^oC, such as, for mesoporous carbon supported molybdenum, total conversion was found at 400^oC.

 

Acknowledgement: Financial support of TUBITAK 214M148 was gratefully acknowledged.