Colloidal Design of Active, Selective, and Stable Catalysts for Methane Utilization

Download or read book Colloidal Design of Active, Selective, and Stable Catalysts for Methane Utilization written by Emmett Daniel Goodman and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to recent advances in locating and extracting natural gas resources, scientists in academia and industry are looking for new processes to take advantage of methane as a chemical precursor and fuel. However, there remain significant challenges in methane utilization; these are related to the strength of methane's carbon-hydrogen bonds, which makes this molecule difficult to activate and utilize. Without a catalyst, methane activation necessitates very high temperatures (~1000 oC), which lead to high energy costs, advanced infrastructure, toxic by-products, and poor product selectivity. Our work focuses on developing catalysts with well-defined structural properties to understand what makes materials active, selective, and stable for methane transformations. To understand which specific nanostructures are best for methane activation, size- and composition- controlled Pt/Pd nanocrystals were designed and studied to reveal the effect of catalyst structure on methane activation. Here, we discuss the effect of these unexplored parameters on methane activation rates, resistance to common catalytic poisons, and changes in oxidation state -- each of which has an important role in contributing to low-temperature activity. Perhaps the greatest challenge in methane activation is selective product formation. In this area, we studied how tuning catalyst support can help selectively produce valuable products (synthesis gas) rather than typical combustion products (carbon dioxide and water). Additionally, we started looking at even more unique nanostructures, involving both organic and inorganic components, for selective methane transformations. The high temperatures needed to activate methane require stable catalysts. By taking advantage of modular colloidal catalyst assembly, we demonstrated synthetic approaches to tune, and measure, the spatial properties of nanocrystal active sites. We found that in many conditions, the spatial properties of active sites determined catalyst stability. In Pd/Al2O3 materials we observed that closer nanocrystals are more stable, in a distant-dependent degradation process. However, in Pd/SiO2 materials we found the opposite - that stability properties are largely distant-independent. Overall, by developing colloidal approaches to catalyst synthesis, we created well-defined catalysts with precisely-controlled sizes, compositions, and spatial properties, which have helped us uncover important design rules for active, selective, and stable methane transformations.