Investigation of catalytic materials for cracking of military aviation fuel to liquefied petroleum gas: High throughput experimentation

The emergence of military technologies powered by liquefied petroleum gas (LPG) necessitates local fuel production at the point of use. LPG provides distinct advantages over batteries as a mobile energy source due to higher gravimetric energy density and longer operating times. For military applications in remote regions, logistical difficulties and harsh practical limitations make it difficult to obtain LPG through conventional distribution channels. If LPG could be derived from readily available fuels such as Jet Propellant-8 (JP-8), a kerosene-based military aviation fuel, then supply-side logistics would be greatly simplified. Developing a method for conversion of JP-8 to LPG is of critical importance to enable increased deployment of LPG powered technologies.;The aim of the current work is to apply a high-throughput approach for the discovery and optimization of catalysts for production of LPG from JP-8 cracking. To accomplish this goal, a high-throughput experimental set-up was retrofitted for processing of liquid hydrocarbon fuels. The focus of this work was design-specific to the needs of a practical military application. Successful catalysts were to exceed a 5% minimum conversion of JP-8 to C 2-C4 hydrocarbons on a mass basis, the fuel could not be desulfurized before reaching the catalyst, and no other system inputs were possible. The challenge of sulfur in JP-8 fuel directed the initial exploratory screening to supported nanoparticle catalysts on oxide supports. It was found that oxide solid acidity, including Lewis acid strength, was of primary importance in determining cracking activity. Furthermore, a γ-Al2O 3 catalyst doped with La produced LPG yields of nearly 10% from JP-8 cracking at a reactor temperature of 650°C.;Aluminosilicate zeolite catalysts having strong solid acidity yielded further improvements in LPG production from JP-8 cracking. ZSM-5 catalysts were optimized for JP-8 cracking activity to LPG through varying reaction temperature and framework Si/Al ratio. The Brønsted acidity of the catalysts and shape-selectivity of the zeolite pore structure contributed to high JP-8 cracking activity. However, the reducing atmosphere required during catalytic cracking resulted in coking of the catalyst and a commensurate decrease in conversion rate. Metal promoters for ZSM-5 catalysts were explored to reduce deactivation and improve coke burnoff regeneration. It was found that rare earth metals reduced the catalyst deactivation rate, and elemental analysis showed less carbon due to coking compared to the base catalyst. Temperature programmed oxidation experiments showed that noble metals reduced onset temperatures for coke burnoff regeneration. A ZSM-5 catalyst promoted with Pt and Gd maintained conversions in excess of 20% on a mass basis at a moderate reactor temperature of 450°C through as many as 14 repeated reaction cycles interspersed with coke burnoff regeneration.;The investigation of carbon burnoff processes on metals hinted at the need for more fundamental catalytic studies involving relatively simple reactions such as CO oxidation on Pt. In molecular-level catalytic investigations, discrepancies that exist between surface science observations under ultra-high vacuum conditions and industrial catalytic performance at higher pressures are referred to as the "pressure gap." Polarization modulation infrared reflection absorption spectroscopy was used to bridge this gap to investigate the adsorption of CO on Pt(100) at near-atmospheric pressures. At a temperature of 325 K, a linear C-O stretch (≈2090 cm-1) was observed, exhibiting linewidth sharpening and a frequency shift of up to ≈6 cm-1 as pressure increased from 1 to 200 Torr CO. A dipole-coupling model was applied to predict CO surface coverages on the Pt(100) surface increasing from ≈0.7 at 1 Torr CO to >0.9 at 200 Torr CO, much greater than similar measurements obtained under UHV conditions. Measurements obtained during reduction from a high-pressure environment indicated that high-pressure adsorption behavior is a mix of reversible and irreversible processes. Spectra of CO adsorbed on Pt(100) exhibited significant broadening and decreasing frequency with increasing sample temperature, consistent with phonon dephasing models for adsorbed CO.;The overall goal of this research work was to demonstrate the utility of a high-throughput approach for systematically accelerating the process of catalyst discovery and optimization. This approach proved highly effective for developing successful catalysts to meet the needs of a fuel processing system for JP-8 cracking to LPG. This work has developed a research framework for investigating complex catalytic processes on a rapid time scale, and the results can be extended to other hydrocarbon-based catalytic cracking systems to create effective energy solutions.