First Principles Investigations of Hydrogen Adsorption on Carbon-Supported Metal Catalysts

Hydrogen is well established as a renewable and clean alternative to conventional fossil fuels and is a potential solution to the global energy crisis. With the ever-rising demand for hydrogen in numerous industries worldwide, there is a clear need for more efficient hydrogen storage methods. In this dissertation, ab-initio density functional theory calculations were performed to extensively investigate both well-ordered and amorphous carbon-based materials for hydrogen adsorption and further metal decoration for possible enhancement in their performance. It was observed that although pristine graphene does not favour spontaneous dissociation and adsorption of hydrogen atoms due to a stable sp2 hybridized structure, local distortions due to defects can cause a change in hybridization to dissociate and adsorb hydrogen spontaneously on certain two-fold coordinated carbon sites. Similarly, the presence of different bonding environments in amorphous carbon structures play an active role in hydrogen adsorption. Hydrogen interacts stronger with two-fold coordinated carbon atoms as compared to three- and four-fold coordinated carbon. High migration barriers for hydrogen atoms on carbon supports make them unlikely to spontaneously spread over the surfaces. To achieve further enhancement, the interaction of metal clusters (Pt and Ni) with these surfaces were considered. It was observed that hydrogen adsorption strength on the carbon atoms of graphene and amorphous carbon increases due to the presence of metal clusters. In addition, the metal support interaction is found to increase with the presence of vacancy defects in the vicinity, which leads to lower energy barriers for hydrogen migration from the metal cluster to the surface. Hydrogen adsorption in a dissociative form on all these surfaces shows a higher saturation limit in the case of Pt clusters as compared to Ni. Overall, metal clusters adsorbed on the carbon supports were proven beneficial for hydrogen adsorption and are crucial to designing efficient materials for H-storage

Adsorption of DNA bases on two?dimensional boron sheets

Utilizing two?dimensional (2D) sheets for DNA fingerprinting applications is an active field of research, with extensive research being carried out on graphene, h?BN and transition metal dichalcogenides. In this theoretical study we propose the newly discovered 2D boron sheets (?, ?1 and ?1 sheets) as a promising adsorbate material for DNA fingerprinting applications. The relatively high binding energies of the DNA bases Adenine (A), thymine (T), guanine (G) and cytosine (C) and the DNA base pairs A:T and G:C on the sheets suggest stabilization of the DNA constructs on these sheets. The stabilization energies were found to be higher in comparison with graphene sheets. The stabilization of the adsorbed nucleobases were found to be mediated by Van?der Waals interaction, with no direct chemical bond being formed between the DNA bases and the sheets, similar to the scenario in graphene and h?BN sheets. Physisorption of the DNA bases was also reflected in the relatively small changes in the work function after adsorption.by Amita Sihag and Sairam S. Mallajosyul

Pt metal supported and Pt4+ doped La1−xSrxCoO3: non-performance of Pt4+ and reactivity differences with Pt metal

In the present work, we correlate the CO-oxidation activity with the oxidation state of platinum with combined experimental and DFT calculations. XPS reveals that Pt supported La1−xSrxCoO3 (Pt/La1−xSrxCoO3) and Pt doped La1−xSrxCoO3 (La1−xSrxCo1−yPtyO3) consist of Pt in 0 and + 4 oxidation states respectively. Further, catalytic CO oxidation over Pt-doped and Pt-supported La1−xSrxCoO3 in the presence of oxygen demonstrates the lowest activity of the doped compound. Pt supported La1−xSrxCoO3 showed the highest activity with almost 100% conversion at 150 °C. La1−xSrxCo1−yPtyO3 was slightly inferior to the blank La1−xSrxCoO3 suggesting that Pt4+ is an inactive or non-performing entity in the doped compound. Temperature programmed desorption (TPD) demonstrates the low amount of CO desorption from La1−xSrxCoO3 and Pt-doped La1−xSrxCoO3 due to the very weak interaction. On the other hand, Pt-supported La1−xSrxCoO3 shows a substantial amount of CO desorption due to strong interaction and large number of metallic sites available for adsorption. This was supported by density functional theory (DFT) based calculations which showed that Pt-supported La1−xSrxCoO3 surface has higher binding energy of CO than the La1−xSrxCoO3 surface confirming the strong CO interaction. Transient responses using mass spectrometer suggest that the Pt supported perovskite utilizes the lattice oxygen for the reaction and vacancies are formed which gets filled with gaseous oxygen. No such phenomenon is observed in the doped compound demonstrating the mechanistic differences in the two catalysts. Often, during the synthesis of Pt-based compounds, it is common to get mixed phases of platinum including Pt4+. From this study, it can be established that one can discard the contribution from Pt4+ in the calculations of kinetic data such as rate or turnover number because this oxidation state is inactive/nonperforming.by Anuj Bisht, Amita Sihag, Akkireddy Satyaprasad,Sairam S. Mallajosyala and Sudhanshu Sharm