Publications

High throughput experimentation has the capability to generate massive, multidimensional datasets, allowing for the discovery of novel catalytic materials. Here, we show the synthesis and catalytic screening of over 100 unique Ru-Metal-K based bimetallic catalysts for low temperature ammonia decomposition, with a Ru loading between 1–3 wt% Ru and a fixed K loading of 12 wt% K, supported on γ-Al2O3. Bimetallic catalysts containing Sc, Sr, Hf, Y, Mg, Zr, Ta, or Ca in addition to Ru were found to have excellent ammonia decomposition activity when compared to state-of-the-art catalysts in literature. Furthermore, the Ru content could be reduced to 1 wt% Ru, a factor of four decrease, with the addition of Sr, Y, Zr, or Hf, where these secondary metals have not been previously explored for ammonia decomposition. The bimetallic interactions between Ru and the secondary metal, specifically RuSrK and RuFeK, were investigated in detail to elucidate the reaction kinetics and surface properties of both high and low performing catalysts. The RuSrK catalyst had a turnover frequency of 1.78 s−1, while RuFeK had a turnover frequency of only 0.28 s−1 under identical operating conditions. Based on their apparent activation energies and number of surface sites, the RuSrK had a factor of two lower activation energy than the RuFeK, while also possessing an equivalent number of surface sites, which suggests that the Sr promotes ammonia decomposition in the presence of Ru by modifying the active sites of Ru.

The synthesis of nanomaterials with well-controlled morphologies and surface orientations has opened new avenues towards increasing catalytic performance and understanding of fundamental catalytic pathways. Here, we illustrate how tailoring surface orientations of Co3O4 catalysts on the nanoscale results in control over catalytic performance via the preferential formation of active surface species during CO2 hydrogenation. This results in a significant increase in the methane yield on Co3O4 nanorods, as opposed to conventional nanoparticle catalysts, where Co3O4 nanorods inhibit the formation of formate spectator species via the preferential formation of bridged CO as an intermediate species. This design approach provides a new dimension for the development of next generation catalysts and opens new, more efficient strategies for the conversion of carbon dioxide into useful hydrocarbons.

Passive selective catalytic reduction (SCR) is a promising approach for the control of NOX emissions in lean burn gasoline exhausts. It requires ammonia (NH3) to be produced over a three-way catalyst (TWC) during periods of fuel-rich operation for the reduction of NOX during periods of fuel-lean operation. Previous research has shown the viability of this system but has not examined the effects of hydrothermal degradation. This work is focused on evaluating the effects of hydrothermal aging on the TWC in a passive SCR system. Two catalysts were studied: a Pd-TWC, and a NOX storage and reduction (NSR) TWC. Samples were aged at 920 °C for 100 h using a four-mode hydrothermal aging procedure. This causes the catalyst to be oxidized and reduced, as it would in a real system. The effects of aging were evaluated using simulated exhaust under both steady state and lean-rich cycling conditions. Hydrothermal aging caused significant changes in catalyst activity, leading to a decrease in low temperature conversion of carbon monoxide (CO) and propane (C3H8) on both catalysts, and degradation of oxygen storage and NOX storage components. However, the catalysts maintained their activity for NOX conversion and NH3 production, showing sufficient activity for the operation of a passive SCR with an optimum projected fuel consumption of 92–98% compared to stoichiometric operation.

Corn residue pellets were torrefied with wet flue gas, simulated by steam (0–21% v/v), CO2 (12% v/v), and O2 (4% v/v), balanced with N2 as reactive gas, in a fixed bed reactor at 260 °C of temperature and at 10–40 min of residence time. The distribution and yields of torrefied pellets, liquid, and gas products were examined. The microstructural changes of torrefied pellets were evaluated by Raman spectroscopy and scanning electron microscopy, while the components of gas products were analyzed by mass spectrometry. Residence time and steam concentration in the reactive gas were found to have significant effects on the products yield distribution, the porosity of the torrefied pellets, and the concentrations of CO, CH4, H2, and CO2 in the gas products. At high steam concentrations, the decomposition reaction of hemicellulose and lignin in the raw pellets, and the formation of the graphene structures in torrefied pellets occurred faster.

Tri-reforming of methane (TRM) produces syngas by directly utilizing flue gas from a fossil fuel-fired power plant without requiring post-combustion CO2 separation. In this work, different yolk sizes of a NiCe@SiO2 multi–yolk–shell nanotube catalyst were prepared and their catalytic properties were evaluated at different oxidizer (CO2 + H2O + O2) to methane (O/M) feed ratios for TRM. The NiCe@SiO2 multi–yolk–shell nanotube catalyst can exhibit longer stability than the conventional NiCe/SiO2Imp catalyst synthesized by impregnation method due to its controlled morphology and synergetic interactions of Ni–Ce and Ni–Si species. At a low O/M feed ratio of 1.0, NiCe@SiO2 with smaller yolks (< 20 nm) shows higher resistance to carbon deposition than NiCe@SiO2 with larger yolks due to the facile oxidation of carbon. On the other hand, NiCe@SiO2 with larger yolks (> 30 nm) presents stable TRM activity at a high O/M feed ratio of 1.1, whereas NiCe@SiO2 consisting of smaller yolks deactivates. Deactivation of NiCe@SiO2 with smaller yolks can be explained by the re-oxidation of active Ni species, in which carbon formation and oxidation rates, and Ce3+/Ce4+ redox properties play a crucial role. Our results indicate that the NiCe@SiO2 multi–yolk–shell nanotube structures can provide high TRM activity, yet their structure should be tuned for stable performance by considering the yolk sizes and interaction of Ni–Ce species.

In this work, a statistical design and analysis platform was used to develop cobalt oxide based oxidation catalysts prepared via one pot metal salt reduction. An emphasis was placed upon understanding the effects of synthesis conditions, such as heating regimen and Co2+ concentration on the metal salt reduction mechanism, the resultant nanomaterial properties (i.e., size, crystal structure, and crystal faceting), and the catalytic activity in CO oxidation. This was accomplished by carrying out XRD, TEM, and FTIR studies on synthesis intermediates and products. Additionally, high-throughput experimentation was employed to study the performance of Co3O4 oxidation catalysts over a wide range of reaction conditions using a 16-channel fixed bed reactor equipped with a parallel infrared imaging system. Specifically, Co3O4 nanomaterials of varying properties were evaluated for their performance as CO oxidation catalysts. Figure-of-merits including light-off temperatures and activation energies were measured and mapped back to the catalyst properties and synthesis conditions. Statistical analysis methods were used to elucidate significant property-activity relationships as well as the design rules relevant in the synthesis of active catalysts. It was found that the degree of grain boundary consolidation and anisotropic growth in fcc and hcp CoO intermediates significantly influenced the catalytic activity. By utilizing the discovered synthesis-structure-activity relationships, CO oxidation light off temperatures were decreased to < 90°C.