Publications

Selective removal of oxygen from biomass-derived polyols is critical toward bridging the gap between biomass feedstocks and the production of commodity chemicals. In this work, we show that earth-abundant molybdenum oxide based heterogeneous catalysts are active, selective, and stable for the cleavage of vicinal C–O bonds in biomass-derived polyols. Catalyst characterization (Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)) shows that partially reduced MoO_x centers are responsible for C–O bond cleavage and are generated in situ by hydrogen dissociated atoms over palladium (Pd) nanoparticles. We find that the support, TiO₂, facilitates communication between the hydrogen dissociating metal and dispersed MoO_x sites through hydrogen spillover. Reactivity studies using a biomass-derived model substrate (1,4-anhydroerythritol) show the effective removal of vicinal hydroxyls over MoO_x-Pd/TiO₂ producing tetrahydrofuran with >98% selectivity at 29% conversion. Catalyst stability is demonstrated upon cycling. These studies are critical toward the development of low-cost heterogeneous catalysts for sustainable hydrodeoxygenation of biobased polyols to platform chemicals.

The efficient delivery of reactive and toxic gaseous reagents to organic reactions was studied using metal-organic frameworks (MOFs). The simultaneous cargo vehicle and catalytic capabilities of several MOFs were probed for the first time using the examples of aromatization, aminocarbonylation, and carbonylative Suzuki–Miyaura coupling reactions. These reactions highlight that MOFs can serve a dual role as a gas cargo vehicle and a catalyst, leading to product formation with yields similar to reactions employing pure gases. Furthermore, the MOFs can be recycled without sacrificing product yield, while simultaneously maintaining crystallinity. The reported findings were supported crystallographically and spectroscopically (e.g., diffuse reflectance infrared Fourier transform spectroscopy), foreshadowing a pathway for the development of multifunctional MOF-based reagent-catalyst cargo vessels for reactive gas reagents as an attractive alternative to the use of toxic pure gases or gas generators.

Hydrothermal synthesis of ZSM-5 zeolites with different Si/Al ratios was conducted by using a microwave-assisted heating method. Their characteristics, such as morphology, porosity, acidity, and the catalytic performance for the cracking reaction of military jet fuel JP-8, were compared with ZSM-5 zeolites obtained via a conventional heating synthesis method. The microwave-assisted heating method contributed to bigger crystal sizes of the ZSM-5 zeolite as well as broader mesopore size distribution in the zeolite crystal with the same Si/Al ratio. Acidity analysis revealed ZSM-5 zeolites with similar acid properties could be produced with both heating methods. As the different heating methods attributed to different crystal sizes and roughness of the synthesized ZSM-5 zeolite, which are influenced by the fast crystal growth and consumption of silicon and aluminum precursor during the hydrothermal synthesis, different petroleum gas yields, and paraffinic product selectivity were observed from the ZSM-5 zeolite produced via microwave-assisted heating method.

Commercial aircraft fuel tanks require sealants applied at contact points to prevent leakage or moisture contamination, but cure times for conventional sealants range from hours to days. Thiol-ene ultraviolet (UV) curable sealants have been a proposed material for these applications. However, selecting proper monomers and optimizing synthesis conditions for a figure of merit is an arduous process. Therefore, modeling the adhesive strength of a thiol-ene sealant was performed using a response surface design of experiment (DoE). Two separate crosslinking alkenes were separately combined with a thiol monomer, and a 6 mm thick polymer was synthesized at different cure temperatures, cure times, and with various solid filler material on an aluminum substrate according to a response surface design. The samples were then peeled off the substrate at a 180° angle, and peel strength was measured. The DoE utilized the peel data to derive a multivariable numeric function for the peel strength. Resulting contour data shows the system has not been fully optimized, but trends in the data show that future experiments should lean toward higher cure times and temperatures to maximize peel strength. Additionally, the resulting model equation can predict adhesive strengths near the studied conditions.

The effect of the addition of a Cu/Al₂O₃ catalyst on the product distribution of gas-phase products during torrefaction of pelletized corn residues was investigated at temperatures between 220 and 300 °C. Pelletized corn residues were mechanically mixed with Cu/Al₂O₃ catalyst pellets. The mixture was then thermally treated in a fixed bed reactor for 40 min of residence time at low temperatures of wet flue gas simulated by O₂ (4% v/v), CO₂ (12% v/v), and steam (14% v/v), balanced with N₂. The higher heating value (HHV) of torrefied pellets was also examined within the operating conditions. It was found that torrefaction temperature affected the product distribution, yields, and HHV significantly, while the presence of Cu/Al₂O₃ catalyst pellets promoted the conversion of CO to CO₂ and the production of H₂ from raw biomass pellets via CO oxidation and water-gas shift reactions. This finding provides a favorable outlook for the energy utilization of pelletized agro-residues via torrefaction with wet flue gas as a pretreatment method, in which inexpensive catalysts could be applied to eliminate toxic gases and/or generate valuable hydrogen during the torrefaction process.

The relevance of multidimensional and porous crystalline materials to nuclear waste reme-diation and storage applications has motivated exploratory research focused on materials discovery of compounds, such as actinide mixed-oxoanion phases, which exhibit rich structural chemistry. The novel phase K1.8 Na1.2 [(UO2)BSi4 O12 ] has been synthesized using hydrothermal methods, rep-resenting the first example of a uranyl borosilicate. The three-dimensional structure crystallizes in the orthorhombic space group Cmce with lattice parameters a = 15.5471(19) \AA, b = 14.3403(17) \AA, c = 11.7315(15) \AA, and V = 2615.5(6) \AA3, and is composed of UO6 octahedra linked by [BSi4 O12 ]5− chains to form a [(UO2)BSi4 O12 ]3− framework. The synthesis method, structure, results of Raman, IR, and X-ray absorption spectroscopy, and thermal stability are discussed.

In this study, we elucidate the reaction kinetics for the simultaneous hydrodeoxygenation of xylitol to 1,2-dideoxypentitol and 1,2,5-pentanetriol over a ReOx-Pd/CeO2 (2.0 weight% Re, 0.30 weight% Pd) catalyst. The reaction was determined to be a zero-order reaction with respect to xylitol. The activation energy was elucidated through an Arrhenius relationship as well as non-Arrhenius kinetics. The Arrhenius relationship was investigated at 150–170 °C and a constant H2 pressure of 10 bar resulting in an activation energy of 48.7 ± 10.5 kJ/mol. The investigation of non-Arrhenius kinetics was conducted at 120–170 °C and a sub-Arrhenius relation was elucidated with activation energy being dependent on temperature, and ranging from 10.2–51.8 kJ/mol in the temperature range investigated. Internal and external mass transfer were investigated through evaluating the Weisz–Prater criterion and the effect of varying stirring rate on the reaction rate, respectively. There were no internal or external mass transfer limitations present in the reaction.

Although storage of H2 in various liquid chemicals makes it very attractive for practical applications, production and purification of H2 from decomposition of these chemicals under relatively mild conditions is still challenging. In this work, we reported production of high-purity H2 from NH3 decomposition using a combined packed bed/membrane reactor loaded with Ru-based catalyst. Three types of membranes (modified MFI zeolite membrane, carbon molecular sieve membrane, and Pd/Ag membrane) were employed and compared for H2 production and purification from NH3 decomposition. All these membrane reactors exhibited high NH3 conversion of >99% with H2 recovery of >90% under pressurized NH3 feed of 7 bar. Nevertheless, H2 purity varied because of the different separation performance of these membranes. High H2 purity of >99.999% with <10 ppb NH3 concentration in permeate was achieved using high-quality Pd/Ag membrane reactor. These results suggest a feasible and highly energy efficient option for producing high-purity H2 from NH3 decomposition.

Washcoat-free catalysts capable of operation in high-temperature combustion exhaust streams were produced via anodically oxidized stainless steel mesh catalysts supports with platinum and palladium as the catalytically active species. Except for the least aggressive anodic treatment, this methodology created catalysts that were more active and stable than catalysts prepared without anodic oxidation. In general, increasing the current during anodic oxidation resulted in increased activity at high temperatures, likely by improving surface roughening, which reduced the impact of steam-enhanced sintering. Treatment with acid with relative medium acidity resulted in catalysts with superior activity and stability. This increase in activity at moderate current has been attributed to increased metal uptake and in the platinum to palladium ratio, which increased to nearly a 1:1 ratio for the most active catalysts, as well more oxide growth relative to surface dissolution. Also, the most active catalyst displayed excellent stability during an extended 100-h time-on-stream test.