(298e) Mo Oxide Supported on Sulfated Hafnia: Novel Catalyst for Activation of Propane

Mo oxide supported on sulfated
hafnia: novel catalyst for activation of propane

Ashraf Abedin¹, Swarom Kanitkar¹, Srikar
Bhattar¹, James J. Spivey*¹

¹ 12.0pt;line-height:107%">Cain Department of Chemical Engineering, Louisiana
State University, Baton Rouge, LA, USA

line-height:107%">For the past few decades the production of natural gas in the
U.S. has increased dramatically after the introduction of modern innovations
such as hydraulic fracturing, offshore drilling, and horizontal drilling. Propane,
the third largest constituent of natural gas, has caught significant attention for
it’s conversion towards value added chemicals. Much of the effort has been
devoted to indirect conversion approaches like oxidative dehydrogenation and
partial oxidation catalytic processes. However, there has been much interest in
direct conversion of propane to higher hydrocarbons, by getting rid of any
intermediate steps that require additional energy supply. 

line-height:107%">Propane aromatization is a direct approach to activate
propane and produce higher hydrocarbons like propylene, benzene etc. Pt or Ga
based HZSM-5 catalysts have shown prominent results in literature for propane
aromatization. These are known as bifunctional catalysts, where the metal sites
in their reduced states activate propane to produce alkyl intermediates, which
subsequently can get oligomerized on the Brønsted acid sites provided by
HZSM-5.  In this work Mo is used as the active metal site supported on sulfated
hafnia (SH) - a novel acidic support for this reaction system. Mo oxide is
reduced in situ to form Mo oxycarbides/carbides phase to activate propane. Sulfated
hafnia is homologous to sulfated zirconia, which is a highly acidic support for
alkane activation. Even though the shape selectivity feature of HZSM-5 is not
present in sulfated hafnia, the acidity is believed to be enough to generate
higher hydrocarbons from the alkyl intermediates provided by the Mo sites.

line-height:107%">5% Mo-SH was synthesized via impregnation method before it
was characterized using DRIFTS and ammonia TPD to study the catalytic acidity
after Mo loading. The nature of the active Mo sites was studied by L_III
edge XANES and HR-TEM. Prior to initiating aromatization reaction, the catalyst
was heated up to the reaction temperature under Argon. The catalyst was reduced
under hydrogen for an hour before introducing propane into the reactor system.
Reaction was run for ~700 mins and the products were analyzed using GC-MSD
system. Primary products observed were ethylene, ethane, propylene, butane and
a small amount of benzene. Deactivation occurred primarily due to carbon
deposition, confirmed later by subsequent TPO analysis on spent catalyst.