UC Irvine

CO2 emissions have drastically increased since the first industrial revolution in the 1750’s. Additionally, methane emissions, the second most greenhouse gas, have kept rising since the first measurement in 1983 and have been growing rapidly in the past two years, possibly due to microbial emissions from wetlands or agriculture. These long-lived greenhouse gases significantly impact global climate change. To slow down global warming and achieve the goal of a zero-carbon footprint, many efforts have been made, such as converting greenhouse gases to syngas, using electricity for reactions, and seeking new heating methods for the reactions instead of using fossil fuels to fire the systems to minimize CO2 emissions.Dry reforming of methane (DRM) can be utilized as a sustainable reaction to capture and utilize greenhouse gases. Ni-based supported catalysts have been widely used due to Ni's low cost and high activity. Despite their excellent performance, side reactions such as methane decomposition and Boudouard reaction can cause severe coke formation, leading to catalyst deactivation. Our work reported that both yolk-shell morphology and Pt-Ni interaction in single-atom-alloy (SAA) structures could maintain the DRM activity. However, the effect of morphology and Pt-Ni interaction could not be elucidated. We studied the reaction kinetics of DRM by proposing a detailed elementary reaction mechanism with 12 surface species and 17 elementary steps over the Ptx-NiCe@SiO2 and Pt0.25-NiCe/SiO2WI catalysts. Due to the different DRM activity over the wet-impregnated and yolk-shell structures, we examined multiple reaction models to explain the effect of morphology and Pt-Ni interaction on the DRM activity. Our results show that the reverse Boudouard reaction and dissociative adsorption of CO2 and CH4 are the rate-limiting steps. The desorption of CO* and H* is also critical to products’ yield and selectivity. Compared with the Pt0.25-NiCe/SiO2WI catalyst, the C* removal followed by the fast CO* desorption is more favored on Pt0.25-NiCe@SiO2 SAA, suggesting the reverse Boudouard reaction prevents the catalyst deactivation by coking. The high O* and low H* coverages are observed on Pt0.25-NiCe@SiO2 SAA due to the confined yolk-shell morphology and enhanced Pt-Ni interaction in SAA structures, respectively. Both these effects can lead to facile C* removal in the Pt0.25-NiCe@SiO2 SAA catalyst, leading to a stable DRM activity. To improve the energy consumption of highly endothermic reactions, we investigated a novel heating method, induction heating (IH), often referred to as radio frequency (RF) heating, for ethanol-to-1,3-butadiene (ETB) reaction as an effective and alternate solution for conventional Joule heating. Instead of being obtained from fossil feedstocks, 1,3-butadiene can be produced from the dehydrogenation of ethanol, a sustainable resource from biomass fermentation. However, the commonly used Ostromislensky process for ETB reaction has two steps: 1) ethanol dehydrogenation to acetaldehyde and 2) 1,3-butadiene production from ethanol and acetaldehyde. The two-step reaction requires different temperatures and catalysts, which makes the 1,3-BD production through the Ostromislensky process inefficient when loaded in a single reactor with conventional furnace heating. However, separate reaction temperature zones can be obtained in a single reactor by adjusting the amount of the susceptors with induction heating (IH) so that two-step reactions can be performed in a tandem system to reduce energy consumption and increase selectivity to the desired products. To verify the IH system and its behavior, the first-step reaction, ethanol dehydrogenation to acetaldehyde, was studied prior to the tandem reaction. The dehydrogenation of ethanol can be catalyzed by supported copper catalysts. The reaction is typically carried out at high temperatures, around 250-300 °C, without oxygen. We studied the catalyst activity with IH for the first time and achieved high ethanol conversion and acetaldehyde selectivity at a temperature of 30 ˚C lower than that with conventional furnace heating (CFH). A transport model was applied to design the catalyst bed configuration and improve the catalyst activity, stability, and energy efficiency by minimizing the temperature gradient. The work was then extended to the Ostromislensky process of the ETB with IH in a tandem system, and the C4 selectivity was tuned by individually controlling the reaction temperature and WHSV of each catalyst bed. A high ethanol conversion of 62.9%, acetaldehyde selectivity of 37.5%, and C4 product selectivity of 55.3% were obtained at relatively low reaction temperatures of T1 = 171 ˚C and T2 = 320 ˚C with the tandem system, nine times lower power consumption than the higher reaction temperatures when T1 is 245 ˚C. Our work suggests that applying IH to a tandem system can successfully achieve the two temperature zones inside a single reactor, such that both production and energy efficiency can be improved for a multi-step reaction.