(208g) Gas Phase Butanal Self-Condensation Over Supported MgO and CeZrOx: A Searching for Acid-Tolerant Solid Base Catalysts

Abstract: 

The sustainable biomass
economy requires development of different integral processes to lower the cost
of producing fuels and chemicals form ligno-cellulosic biomass.  Accordingly,
the new concept for the catalytic conversion of the biomass to monofunctional
hydrocarbons and targeted liquid fuels have been provided, where the sugars and
polyols were first converted into small oxygenates over a Pt-Re/C catalyst. 
The development of the limited steps for the upgrading those mono-functional
oxygenates are necessary in order to achieve value added chemicals or fuels.  We
conducted the gas phase butanal self-condensation reactions as a model study
for the carbon-carbon forming reactions.  The unsupported MgO and CeZrO_x
solid solution showed less active for the reaction.  The silica supported MgO,
SrO and a mixture of MgO/SrO catalyst showed improved activity.  However, the
catalysts deactivated very quickly due to the self-poisoning by butanoic acid,
a compound generated through side reactions.  CeZrO_x/SiO₂
showed a promising performance on butanal self-condensation with about 40%
conversion of butanal at 300 ºC and good stability.  The effects of the
reaction temperatures, addition of butanoic acid and supports were studied and
compared over the MgO/SiO₂ and CeZrO_x/SiO₂ catalysts. 
The CeZrO_x/SiO₂ catalyst is much more acid-tolerant
compared with MgO/SiO₂  and lowered the reaction temperature
approximate 100 ºC with the same butanal conversion.  The reaction chemistry
was studied.  The predominate reaction pathway is the aldol condensation of
butanal with about 85% selectivity to first addition product and 6 % selectivity
to second addition products.  The side reactions include Tishchenko
esterification reactions, hydrolysis, ketonizations, isomerizations and
hydrogenation/dehydration reactions.  The nature of the active sizes and the
reaction mechanism were also studied by a combination of TPD and in-situ FTIR
studies.

Keywords:  Butanal
self-condensation; CeZrO_x solid solution; Silica supported CeZrO_x,
supported and unsupported alkaline metal oxide; CO₂-TPD; NH₃-TPD;
in-situ FTIR