(396d) Enhanced Dry Reforming of Methane Using Pseudo Catalytic Metal Oxide and Nanoparticles

As the world is rapidly developing alongside an increasing population, energy demands have risen dramatically. Historically, technological advances have improved human well-being, but many have also unintentionally contributed to environmental degradation and damage to society because of harmful greenhouse gas generation such as CO₂. A significant contribution to this has been the use of fossil fuels over the past two centuries. To ensure that engineering makes net-positive contributions to sustainable and economic process development, especially for reforming fossil fuels, we need approaches to develop technologies that reduce the chance of such unintended harm. Due to fracking or hydraulic fracturing, there has been a steep rise in natural gas production. Large amounts of natural gas are flared because of storage limitations, which leads to energy wastage and engenders a considerable amount of CO₂. Materials that can convert the flared natural gas containing primarily CH₄ into synthesis gas (CO+H₂) by employing CO₂ as the reforming gas have lately received pressing attention. Through this process, the two greenhouse gases CH₄ and CO₂ are utilized, and this reaction is classified as Dry Reforming of Methane (DRM). However, DRM at high temperature where the reactants exhibit maximum conversions faces two major hurdles concerning its catalyst: 1) Carbon deposition on the active metal sites and 2) Sintering of the active metal, which reduces the activity. Several researchers have proposed ways to mitigate these issues, including alternative synthesis techniques, mesoporous supports to prevent agglomeration of the active metal, injection of steam to reduce the amount of carbon, etc. Though, these strategies increase the life of the catalyst but haven’t solved the issue. Consequently, the catalysts fail before 200 hours of operation. Based on our thermodynamic calculations, efforts to curb carbon deposition under typical high-temperature conditions is thermodynamically unattainable.

To address the issue, a higher proportion of CO₂ with respect to methane is investigated. At this ratio, carbon deposition is thermodynamically zero at pressures up to 30 atm, which means the process can be operated even at higher pressures, thus eliminating the enormous compression and decompression costs. A pseudo-catalytic metal-oxide (PMO) prepared using industrial solid state synthesis method is developed to process the higher CO₂ to CH₄ ratio. The pseudo-catalytic nature of the metal oxide is imparted by the PMO’s tendency to participate in the reaction, forming stable reaction intermediates. The PMO material employs a unique syngas generation mechanism at high temperatures to efficiently convert CH₄ and CO₂ to syngas. Based on the demand, this high-quality syngas can be further converted into liquid fuels such as C3+ olefins and aromatics. Continuous testing at 1000C at CO₂/CH₄ ratio of 1.5 exhibited no carbon deposition for more than 850 hours. Further, the process showed 80% CO₂ conversion and near 100% CH₄ conversion during the testing. The syngas yield per mole of CH₄ is 3.7 versus the thermodynamic limit at 3.8. Besides, the quality of syngas obtained is H₂:CO = 0.8. Steam can be added to the reactants to alter the syngas quality further.

Furthermore, smaller size nanoparticles were also studied to investigate the effect of particle size on the reaction performance. The material is based on FeNi₃ nanoparticles supported by SBA-15 (FeNi3@SBA-15). The pore size and pore connectivity of SBA-15 have been tuned to achieve the optimal molecular diffusivity and reactivity. This tuning was achieved by controlling intermicellular interactions, through the choice of surfactant and the synthesis temperature. The FeNi3@SBA-15 samples were synthesized using wet impregnation method and their physicochemical characteristics were analyzed with Brunauer-Emmet-Teller (BET), transmission electron microscopy (TEM), X-ray diffraction (XRD), and small-angel X-ray scattering (SAXS) analyses. Their catalytic activity was studied by temperature-programmed reaction. The FeNi3@SBA-15 with a pore radius of 18.7 Ã… and pore volume of 0.461 cc/g exhibited high reaction kinetics and over 99% methane conversion at 900 ℃. The potentiality of these nanoparticles can be investigated further for long term and high temperature testing similar to industrial grade PMO. Enhanced DRM can be an effective route to utilize the two greenhouse gases, converting them into value-added products.