H2Formation on Cosmic Grain Siliceous Surfaces Grafted with Fe+: A Silsesquioxanes-Based Computational Model.
Cosmic siliceous dust grains are involved in the synthesis of H2in the inter-stellar medium. In this work, the dust grain siliceous surface is represented by a hydrogen Fe-metalla-silsesquioxane model of general formula: [Fe(H7Si7O12-n)(OH)n]+(n=0,1,2) where Fe+behaves like a single-site heterogeneous catalyst grafted on a siliceous surface synthesizing H2from H. A computational analysis is performed using two levels of theory (B3LYP-D3BJ and MP2-F12) to quantify the thermodynamic driving force of the reaction: [Fe-T7H7]++4H→[Fe-T7H7(OH)2]++H2. The general outcomes are: 1) H2synthesis is thermodynamically strongly favored; 2) Fe-H / Fe-H2barrier-less formation potential; 3) chemisorbed H-Fe leads to facile H2synthesis at 20≤T≤100 K; 4) relative spin energetics and thermodynamic quantities between the B3LYP-D3BJ and MP2-F12 levels of theory are in qualitative agreement. The metalla-silsesquioxane model shows how Fe+fixed on a siliceous surface can potentially catalyze H2formation in space.
Department of Chemistry, 213 Smith Chemistry Building, The University of Memphis, Memphis, TN, 38152, USA.|Konrad-Mueller Str. 17, 52249, Eschweiler, Germany.
Marco
http://orcid.org/0000-0003-0421-5351
M
Fioroni
Department of Chemistry, 213 Smith Chemistry Building, The University of Memphis, Memphis, TN, 38152, USA.
Nathan J
NJ
DeYonker
astrochemistry; computational chemistry; heterogeneous catalysis; hydrogen; supported catalysts