THE CATALYST REVIEW - The Catalyst Group

PROCESS NEWS
Scientists Figure Out Way to Convert CO 2
Into
Carbon Monoxide Using Visible Light…
A team of scientists has figured out a way to efficiently turn carbon dioxide (CO 2
)
into carbon monoxide using visible light, like sunlight. The method was developed by
University of Michigan biological chemist Steve Ragsdale, along with research assistant
Elizabeth Pierce and scientists led by Fraser Armstrong from the University of Oxford in
the UK. Ragsdale and his associates succeeded in using an enzyme-modified titanium
oxide to get carbon dioxide's electrons excited and willing to jump to the enzyme, which
then catalyzes the reduction of carbon dioxide to carbon monoxide. A photosensitizer
that binds to the titanium allows the use of visible light for the process. The enzyme is
more robust than other catalysts, willing to facilitate the conversion again and again.
The trick is that it can't come near oxygen. "By using this enzyme, you put it into a
solution that contains titanium dioxide in the presence of a photosensitizer," Ragsdale
said. The direct product - carbon monoxide - is a desirable chemical that can be used
in other processes to produce electricity or hydrogen. Carbon monoxide also has
significant fuel value and readily can be converted by known catalysts into hydrocarbons
or into methanol for use as a liquid fuel. Not only is it a demonstration that an abundant
compound can be converted into a commercially useful compound with considerably
less energy input than current methods, it also is a method not so different from what
organisms regularly do. Source: newKerala online, 3/9/2010.
Refined Path from Biomass to Biofuel…
The challenge of economically converting lignocelluosic biomass into transportation
fuels is to develop efficient chemistry that minimizes processing. In a bid to meet
that challenge, Jesse Q. Bond, James A. Dumesic, and coworkers at the University of
Wisconsin, Madison, have devised an integrated flow-reactor system for converting the
versatile biomass-derived feedstock γ-valerolactone into ready-to-use gasoline and jet
fuel. The Wisconsin team’s method improves downstream processing of γ-valerolactone
by first using a silica-alumina catalyst to open the ring and decarboxylate aqueous
γ-valerolactone to a mixture of butenes and CO 2
. The butenes are subsequently strung
together by using an amberlyst catalyst to form octenes and higher alkene oligomers
with molecular weights and branching that can be selectively formulated as gasoline
or jet fuel. The new approach provides several bonuses. It avoids costly preciousmetal
catalysts and doesn’t require an external source of H 2
. And although the process
generates CO 2
as a by-product, the reactor design allows the CO 2
to be trapped as a
relatively pure, pressurized stream that could be readily sequestered or used to make
methanol or polycarbonates. Source: Chemical & Engineering News, 3/1/2010, p. 34.
Thin Sheets of ZSM-5 Constitute Zeolite
Membrane…
Researchers from Osaka Prefecture University, Stockholm University and the Korea
Advanced Institute of Science and Technology (KAIST) have synthesized sheets of
ZSM-5 (MFI type) zeolites that are only 2 nm thick, which corresponds to the b-axis
dimension of a single MFI unity cell. The sheet structure is said to improve the surfaceto-volume
ratio compared to conventional zeolite catalysts: the larger number of acid
sites on the external surface of the zeolite sheets have been demonstrated to impart
a higher catalytic activity for the cracking of large organic molecules. The reduced
crystal thickness also facilitates diffusion, thereby dramatically suppressing catalyst
deactivation through coke deposition during methanol-to-gasoline conversion, says
Osaka’s Yasuhiro Sakamoto. The scientists believe the synthesis approach – which
involves crystallization in bifunctional surfactants – could be applied to make other
zeolites with improved catalytic performance. Source: Chemical Engineering, 2/2010.
Co-Catalyst Tag
Team…
Adding a chiral urea’s embrace to a
ring-forming reaction catalyzed by an
achiral Brønsted acid renders the process
highly enantioselective, chemists at
Harvard University have found. The
work could inspire a general strategy
for using organocatalysts to perform
enantioselective transformations on
cations. Several teams have already
used “cooperative catalysis” that pairs
a metal catalyst or organocatalyst
with a cocatalyst to achieve selective
bond formations. Eric N. Jacobsen and
colleagues have now applied that school
of thought to a strong acid-catalyzed
cycloaddition that forms a heterocyclic
motif common in bioactive compounds.
On its own, the Brønsted acid reacts with
an imine substrate to form a reactive
cationic intermediate, leading to a fast
but nonselective reaction. But add the
chiral urea, and things change, according
to the team’s kinetic, spectroscopic, and
computational data. The urea interacts
with the cation via a network of hydrogen
bonds and a π-π interaction. Effectively,
this enzyme-like strategy slows the
reaction and blocks one face of the
cation, permitting formation of only one
enantiomer, Jacobsen says. The team
plans to extend this controlled reactivity
to other classes of cations. Source:
Chemical & Engineering News, 2/22/2010,
p. 35.
In a computer model, a chiral urea (blue)
binds the anion of a Brønsted acid (yellow)
and blocks one face of the cation (red) in a
cycloaddition, allowing a reaction partner
(green) to approach from only one side.
The Catalyst Review March 2010
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