2014 AIChE Annual Meeting

November 16th - November 21th, 2014

Hilton Atlanta

Atlanta, GA

Program Topic: 20023 Catalysis with Microporous and Mesoporous

Title: Preparation of isolated iron species in ZSM-5 for high selectivity alcohol formation from lower alkanes under mild conditions

Presenting Author: Michael M Forde§,¥ Email: michael.forde@sta.uwi.edu

Co-Authors:

Robert Armstrong§ Email: ArmstrongR4@cardiff.ac.uk Peter Wells� Email: peter.wells@rc-harwell.ac.uk Nikoloas Dimitratos§ Email: DimitratosN@cardiff.ac.uk Graham J Hutchings§ email: Hutch@cardiff.ac.uk
Christopher J Kiely* Email: chk5@Lehigh.edu
Qian He* Email: heqian.lehigh@gmail.com

§ Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Main Building Park Place, Cardiff, CF103AT , United Kingdom. Tel.: +442920874059

Â¥ Department of Chemistry, University of the West Indies, St. Augustine Campus, Trinidad and

Tobago. Tel: +18686622002 ext83544

* Department of Materials Science and Engineering, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015-3195, USA.

â?  UK Catalysis Hub, Research Complex at Harwell, Rutherford Appleton Laboratory, R92, Harwell Science & Innovation Campus, Didcot, United Kingdom OX11 0FA

Abstract

The utilisation of iron species in ZSM-5 for selective catalytic conversion of methane to methanol and benzene to phenol, as well as nitrous oxide decomposition has been researched for decades. The traditional routes to the incorporation of iron (and other heteroatoms) in ZSM-5 encompass hydrothermal synthesis with iron in the gel mixture and post-preparation methods such as liquid phase ion exchange, solid state ion exchange and wet impregnation. In many of these routes it has been shown that the form of the deposited iron depends on the iron loading, presence of water/other solvents in the preparation process and the post-preparation heat treatments performed to activate the materials. Commonly agglomerated iron species (iron oxides) are formed after high temperature heat treatment by the dislodging of iron initially from as framework species (tetrahedral coordination) or extra-framework iron ions/complexes. We have employed chemical vapour impregnation (CVI) to prepare highly dispersed isolated iron species with the channels and cages of ZSM-5(30). These species primarily show octahedral coordination with a primary coordination sphere consisting solely of oxygen neighbours which is in contrast of all previous reports that postulate iron/aluminium and oxygen in the primary coordination sphere. We consider our iron species to be located at cationic exchange sites in the material but not formally linked to the framework, which is a major deviation from conventional active site models. Our prepared catalysts (heat treated under reducing atmospheres) show high selectivity towards methanol and ethanol formation from methane and ethane respectively using hydrogen peroxide as the oxidant under mild conditions in contrast to the materials which are prepared by traditional methods or heat treated in air. We link this important observation to formation of the isolated iron species in the materials. We will show that the materials are reusable and achieve direct conversion of ethane to ethanol, unlike or previously proposed mechanisms (for air treated materials) which show that the alcohol product is derived from a hydroperoxy intermediate in the reaction.