Density functional theory study of structure, electronic and magnetic properties of non-metal (Group 13) doped stable $$\hbox {Rh}_{\mathrm{n}}({\mathrm{n}}=2{-}8)$$ Rh n ( n = 2 - 8 ) clusters and their catalytic activities towards methanol activation

Abstract

Rhodium clusters are very important finite size materials because of their unique electronic, magnetic and catalytic properties. Tuning the physical and chemical properties of rhodium clusters by incorporating different metal and non-metal atoms have found a great research interest in recent years. In this study, non-metal atoms of group 13, viz., B, Al or Ga were incorporated into the stable rhodium clusters to evaluate the structure, stability, electronic, magnetic as well as catalytic properties using density functional theory (DFT). Stability function, dissociation energy and LUMO-HOMO gap analysis reveal the higher stability of $$\hbox {Rh}_{5}\hbox {B}$$ , $$\hbox {Rh}_{4}\hbox {Al}$$ and $$\hbox {Rh}_{4}\hbox {Ga}$$ clusters. Boron-doped on even-atomic rhodium clusters are more stable than odd-atomic rhodium clusters whereas both odd and even-atomic clusters were found to be stable for Al and Ga-doped rhodium clusters. Deformed electron density was found to be higher in the case of $$\hbox {Rh}_{5}\hbox {B}$$ , $$\hbox {Rh}_{4}\hbox {Al}$$ , $$\hbox {Rh}_{7}\hbox {Al}$$ and $$\hbox {Rh}_{4}\hbox {Ga}$$ clusters along all the bonds as well as at the atoms, which indicates higher stability of these non-metal doped rhodium clusters. LUMO and HOMO orbital analysis suggests that electronic redistribution occurs from HOMO (Rh) to LUMO (non-metal). DOS and COOP studies reveal the higher contribution of d electrons in the bonding region rather than s and p electrons. Spin density and magnetic moment analysis indicate zero magnetic moment for even-atomic B, Al or Ga-doped rhodium clusters due to the cancellation of spin up and spin down densities, whereas for the odd ones the magnetic moment is non-zero. Greater catalytic activity for the activation of methanol is noticed with $$\hbox {Rh}_{4}\hbox {Al}$$ and $$\hbox {Rh}_{4}\hbox {Ga}$$ in comparison to $$\hbox {Rh}_{5}$$ , while the activity with $$\hbox {Rh}_{5}\hbox {B}$$ is lower. In this study B or Al or Ga are incorporated into pure rhodium clusters to evaluate the structural, electronic and magnetic properties using density functional theory. Structural and electronic parameters reveal the higher stability of $$\hbox {Rh}_{5}\hbox {B}$$ , $$\hbox {Rh}_{4}\hbox {Al}$$ and $$\hbox {Rh}_{4}\hbox {Ga}$$ clusters. Also, these doped clusters show methanol activation.