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H2 Formation on Cosmic Grain Siliceous Surfaces Grafted with Fe+: A Silsesquioxanes‐Based Computational Model
Authors:Dr Marco Fioroni  Prof?Dr Nathan J DeYonker
Institution:1. Department of Chemistry, 213 Smith Chemistry Building, The University of Memphis, Memphis, TN, USA;2. , Eschweiler, Germany
Abstract:Cosmic siliceous dust grains are involved in the synthesis of H2 in 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 H2 from 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) H2 synthesis is thermodynamically strongly favored; 2) Fe‐H / Fe‐H2 barrier‐less formation potential; 3) chemisorbed H‐Fe leads to facile H2 synthesis 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 H2 formation in space.
Keywords:astrochemistry  computational chemistry  heterogeneous catalysis  hydrogen  supported catalysts
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