UC Riverside

The development of Single Atom Catalysts (SACs) is a milestone in the catalysis industry. SACs usually have unique electronic properties and ultrahigh reactivity for chemical reactions. The Turnover frequency (TOF) values of SACs are generally much larger than that of regular nanoparticle catalyst. However, due to the high surface energy of the SACs, the aggregation effect restrains the researchers from further increasing the loading of the single atoms over the supports. The aggregation, not like the coking which could be easily solved by reoxidation of the catalyst, is irreversible and would also lead to the deactivation of the catalyst. This conundrum prevents the implementation of SACs in industrial usage. To solve this problem, scientists usually leverage the Strong Metal-Support interaction (SIMI) effect to anchor the single atoms by the defect sites on the support (e.g., vacancies, hydroxyl group). In this dissertation, the first part of our work is to conduct the rational design of the SACs on the 2-dimensional (2D) hexagonal boron nitride (h-BN) materials. We assessed the possibility of noble metals Ru, Pt, and Au loaded on h-BN as SACs from three aspects (i.e., stability, activity, and selectivity). Both ab initio Molecular Dynamics (AIMD) simulations and anchoring energy calculations suggested that Au is not stable over the defect sites of h-BN. From the reaction energy plot of the propane dehydrogenation (PDH), we found that the Pt over B vacancy and Ru over N vacancy are promising for PDH reactions with low dehydration barriers. We also found that there is a trade of for the C-H bond activation and C3H6 desorption. This trade-off relationship let the researchers make a compromise between the activity and selectivity when conducting the catalyst design. The second part of this thesis focuses on the activity of the defect sites of the h-BN, we selected a set of vacancy sites with different sizes. From the defect formation energy calculations, we found that the normalized formation energy decreases with the increase of defect size. Also, we probed the CH4 activation over these vacancies and we found that the B-B pair over the N vacancy and B-N pair over the BN2 vacancy have excellent reactivity for CH4 activation. The third part of our work is to examine the activity and selectivity of CH4 oxidation to acetic acid reaction over single atom Rh dispersed Porphyrin-based Metal Organic Framework (pMOF) catalyst. We found that the Rh in-plane model favors the CH3OH formation while the Rh out-of-plane model favors the CH3COOH formation. This thesis gives the interpretation of the reaction mechanism of single atom catalysts over h-BN and pMOF catalysts.