Darrin S. Muggli

Photocatalytic decomposition of acetic acid on TiO2

During room‐temperature transient experiments, acetic acid decomposes photocatalytically on TiO2 in an inert atmosphere by two parallel pathways. One pathway forms CO2 and C2H6 in a 2:1 ratio, and H2O forms with lattice oxygen that was extracted from the surface. The other pathway forms CO2 and CH4 in a 1:1 ratio.

Improved Catalyst for Photocatalytic Oxidation of Acetaldehyde Above Room Temperature

Sulfated TiO2 was more active and deactivated more slowly than Degussa P-25 TiO2 during PCO of acetaldehyde above 373 K. Thermal catalytic reactions appear to poison both catalysts. Sulfating TiO2 increased surface area by 60% and increased the number of acetaldehyde adsorption sites by a factor of 1.7.

AROMATIZATION OF PROPYLENE OVER HZSM-5: A DESIGN OF EXPERIMENTS (DOE) APPROACH

Aromatization of propylene was performed in a continuous reactor over HZSM-5 catalysts. A full-factorial design of experiments (DOE) methodology identified the effects of temperature (400°–500°C), Si:Al ratio (50–80), propylene feed concentration (8.9–12.5 mol.%), and catalyst amount (0.2–1.0 g) on propylene conversion as well as the yields of benzene, toluene, p-xylene, o-xylene (BTX), and total BTX. The Si:Al ratio and amount of the HZSM-5 catalyst influenced all of the responses, while temperature affected all the responses except the yield of p-xylene. An increase in feed concentration significantly increased the yields of benzene, toluene, and total BTX. An interaction between propylene feed concentration and catalyst amount influenced the yields of benzene, toluene, and total BTX. This interaction indicated that a higher feed concentration promotes aromatization at higher catalyst concentrations. By contrast, the interaction of Si:Al ratio with propylene feed concentration was found significant for p-xylene and o-xylene yields, but not for benzene and toluene, suggesting that xylenes are synthesized on different sites than those for benzene and toluene. These interaction effects demonstrate how the use of DOE can uncover significant information generally missed using traditional experimental strategies.

Photocatalytic Oxidation of Dichloroacetic Acid and Dichloroacetyl Chloride on TiO2: Active Sites, Effect of H2O, and Reaction Pathways

Photocatalytic oxidation (PCO) quickly oxidizes dichloroacetyl chloride and dichloroacetic acid to phosgene (COCl2) and CO2 on TiO2. At least two types of active sites exist for PCO on TiO2 and their activities differ by more than an order of magnitude; the more-active sites comprise approximately 30 of the adsorption sites. Water redistributes adsorbed dichloroacetyl chloride and dichloroacetic acid to more-active sites during transient PCO, yet does not change PCO activity or selectivity. Dichloroacetyl chloride oxidizes through parallel pathways, one of which forms dichloroacetic acid as an intermediate. The α-carbon in dichloroacetic acid quickly oxidizes to CO2 without forming any long-lived intermediates, whereas the β-carbon forms CO2 and COCl2 in parallel reactions.

Extraction of Fatty Acids from Noncatalytically Cracked Triacylglycerides with Water and Aqueous Sodium Hydroxide

A study was performed to determine the effectiveness of extracting short-chain fatty acids (SCFAs) from noncatalytically cracked canola oil using neutral and basic aqueous solutions. A detailed quantitative analysis was performed to determine the composition of the cracking reactor organic liquid product (OLP) before and after extraction. We have demonstrated that water alone can be used to completely extract C2 and C3 monocarboxylic acids, while partially extracting acids up to C6. The degree of extraction can be slightly increased by increasing temperature and, for some acids, by using multiple extraction stages. A basic solution (1 M NaOH) was found to extract a wider range of acids—up to C8—and this was independent of the temperature or number of stages. While this method was not capable of reducing the acid number of the OLP to within the specifications for fuel, it could be used to extract a narrow range (C2 to C5) of biobased carboxylic acids. As such, this method could serve as one step in a process to produce biobased carboxylic acids, replacing acids currently produced from non-renewable sources.

SYNTHESIS FACTORS THAT IMPACT TiO2 NANOTUBE ACTIVITY DURING GAS-PHASE PHOTOCATALYTIC OXIDATION OF METHANOL

Statistically designed experiments determined which steps in the hydrothermal synthesis of TiO2 nanotubes significantly impacted the rate of photocatalytic oxidation of gas-phase methanol. This study investigated the following synthesis steps: sodium hydroxide treatment time, conductivity of the first and second washings, acid treatment time and pH, calcination temperature, and H2O2 post-treatment. The synthesis procedure produced a highly active photocatalyst; the maximum catalyst activity of the TiO2 nanotubes was approximately seven times that of the starting material, Degussa P-25. Characterization with transmission electron microscopy, X-ray diffraction, and temperature-programmed oxidation revealed that the nanotubes were 10–12 nm in diameter with an average length of approximately 100 nm.

A high-throughput reaction system to measure the gas-phase photocatalytic oxidation activity of TiO2 nanotubes.

A sixteen-channel, high-throughput system was designed and built to test the activity of catalysts for gas-phase photocatalytic oxidation of methanol. The system utilizes granular catalyst films to model relevant applications and allow for rapid processing. It is capable of 48 catalyst tests per day using the procedure described herein. Several experiments were performed to minimize both the within-node and between-node variances of the system. Utilizing the high-throughput system, the significance of preparation methods on the photocatalytic activity of TiO2 nanotubes was investigated. A one-half fractional factorial experiment identified the factors that significantly impact catalyst activity as the following: precursor type (Degussa P-25, or nanotubes), platinum loading, the interaction between precursor and dope time, and the interaction between the precursor and calcination temperature. Based on experimental results, catalyst activity is optimized by doping TiO2 nanotubes directly (rather than doping P-25 prior to nanotube formation), a low platinum loading (0.01 wt %), and using a dope time of 30 min followed by calcination at 773 K. The optimum catalyst preparation conditions produced a catalyst that was three times more active than the starting P-25 material.

Mercury Oxidation via Catalytic Barrier Filters Phase II

In 2004, the Department of Energy National Energy Technology Laboratory awarded the University of North Dakota a Phase II University Coal Research grant to explore the feasibility of using barrier filters coated with a catalyst to oxidize elemental mercury in coal combustion flue gas streams. Oxidized mercury is substantially easier to remove than elemental mercury. If successful, this technique has the potential to substantially reduce mercury control costs for those installations that already utilize baghouse barrier filters for particulate removal. Completed in 2004, Phase I of this project successfully met its objectives of screening and assessing the possible feasibility of using catalyst coated barrier filters for the oxidation of vapor phase elemental mercury in coal combustion generated flue gas streams. Completed in September 2007, Phase II of this project successfully met its three objectives. First, an effective coating method for a catalytic barrier filter was found. Second, the effects of a simulated flue gas on the catalysts in a bench-scale reactor were determined. Finally, the performance of the best catalyst was assessed using real flue gas generated by a 19 kW research combustor firing each of three separate coal types.