ACS Omega,
Journal Year:
2021,
Volume and Issue:
6(44), P. 29471 - 29482
Published: Oct. 25, 2021
The
structure
and
evolution
of
Pd
species
in
Pd-exchanged
zeolite
materials
intended
for
use
as
passive
NO
x
adsorbers
were
examined
under
various
pretreatment
conditions.
Using
situ
CO-diffuse
reflectance
infrared
spectroscopy,
structures
characterized
after
500
°C
pretreatments
inert
(Ar),
water
(1-2%
H2O
Ar),
oxidizing
(air),
reducing
(H2,
CO)
atmospheres.
Two
zeolites
similar
Si/Al
ratios
but
different
framework
topologies
(Beta,
CHA)
found
to
show
distributions
species,
depending
on
the
agent
used.
Reduction
H2
(500
°C;
10%
Ar)
followed
by
re-oxidation
air)
led
higher
amounts
single-site
ions
Pd-CHA
than
Pd-Beta,
whereas
high-temperature
reduction
CO
1000
ppm
significant
loss
ionic
both
albeit
temperature-programmed
XPS
experiments
suggest
that
this
phenomena
may
be
limited
surface
Pd.
High-temperature
treatments
with
1-2%
are
shown
form
either
metal
or
PdO
particles,
Pd-Beta
being
more
susceptible
these
effects
Pd-CHA.
This
work
suggests
especially
problematic
respect
durability
adsorption
applications,
case
Beta
zeolite.
Journal of the American Chemical Society,
Journal Year:
2024,
Volume and Issue:
146(12), P. 8280 - 8297
Published: March 11, 2024
Single-site
copper-based
catalysts
have
shown
remarkable
activity
and
selectivity
for
a
variety
of
reactions.
However,
deactivation
by
sintering
in
high-temperature
reducing
environments
remains
challenge
often
limits
their
use
due
to
irreversible
structural
changes
the
catalyst.
Here,
we
report
zeolite-based
copper
which
oxide
agglomerates
formed
after
reaction
can
be
repeatedly
redispersed
back
single
sites
using
an
oxidative
treatment
air
at
550
°C.
Under
different
environments,
single-site
Cu–Zn–Y/deAlBeta
undergoes
dynamic
structure
oxidation
state
that
tuned
promote
formation
key
active
while
minimizing
through
Cu
sintering.
For
example,
Cu2+
reduces
Cu1+
catalyst
pretreatment
(270
°C,
101
kPa
H2)
further
Cu0
nanoparticles
under
conditions
(270–350
7
EtOH,
94
or
accelerated
aging
(400–450
H2).
After
regeneration
°C
air,
agglomerated
CuO
was
dispersed
presence
absence
Zn
Y,
verified
imaging,
situ
spectroscopy,
catalytic
rate
measurements.
Ab
initio
molecular
dynamics
simulations
show
solvation
monomers
water
facilitates
transport
zeolite
pore,
condensation
monomer
with
fully
protonated
silanol
nest
entraps
reforms
structure.
The
capability
nests
trap
stabilize
oxidizing
could
extend
wider
reactions
allows
simple
strategy
catalysts.
ACS Catalysis,
Journal Year:
2022,
Volume and Issue:
12(9), P. 5060 - 5076
Published: April 14, 2022
Zeolites
and
metal-zeolites
are
a
class
of
porous
materials
that
have
been
widely
utilized
in
industry.
So
far,
several
fundamental
questions
relating
to
the
dynamic
evolution
zeolite
framework
metal-zeolite
interface
remain
unanswered.
Contrary
classical
view
zeolites
as
static,
rigid,
changeless
material,
atoms
foreign
metals
can
dynamically
interconvert
under
pretreatment
or
reaction
conditions,
making
it
difficult
identify
real
active
centers
mechanisms.
With
development
characterization
techniques
theoretical
calculations,
more
profound
understanding
at
atomic
scale
has
achieved.
This
critical
Review
will
feature
recent
progress
metal-zeolites,
mainly
focusing
on
T–O–T
bonds
breaking
formation,
metal
valence
state
transformation,
phase
evolution,
migration.
We
compare
these
proposed
mechanisms
analyze
their
suitability
distinct
experimental
conditions.
highlight
identification
sites
catalytic
mechanism
should
be
cautious
consider
Finally,
we
summarize
usages
limitations
different
characteristic
techniques,
propose
some
future
research
directions
about
hope
bridge
gaps
between
knowledge
achieved
characterizations
nature
guide
zeolite-based
synthesis,
modification,
application.
Environmental Science & Technology,
Journal Year:
2023,
Volume and Issue:
57(9), P. 3467 - 3485
Published: Feb. 21, 2023
It
remains
a
major
challenge
to
abate
efficiently
the
harmful
nitrogen
oxides
(NOx)
in
low-temperature
diesel
exhausts
emitted
during
cold-start
period
of
engine
operation.
Passive
NOx
adsorbers
(PNA),
which
could
temporarily
capture
at
low
temperatures
(below
200
°C)
and
release
stored
higher
(normally
250–450
downstream
selective
catalytic
reduction
unit
for
complete
abatement,
hold
promise
mitigate
emissions.
In
this
review,
recent
advances
material
design,
mechanism
understanding,
system
integration
are
summarized
PNA
based
on
palladium-exchanged
zeolites.
First,
we
discuss
choices
parent
zeolite,
Pd
precursor,
synthetic
method
synthesis
Pd-zeolites
with
atomic
dispersions,
review
effect
hydrothermal
aging
properties
performance
Pd-zeolites.
Then,
show
how
different
experimental
theoretical
methodologies
can
be
integrated
gain
mechanistic
insights
into
nature
active
sites,
storage/release
chemistry,
as
well
interactions
between
typical
components/poisons
exhausts.
This
also
gathers
several
novel
designs
modern
exhaust
after-treatment
systems
practical
application.
At
end,
challenges,
important
implications,
further
development
real
application
Pd-zeolite-based
mitigation.
Journal of the American Chemical Society,
Journal Year:
2022,
Volume and Issue:
144(30), P. 13874 - 13887
Published: July 19, 2022
Catalysts
composed
of
platinum
dispersed
on
zeolite
supports
are
widely
applied
in
industry,
and
coking
sintering
during
operation
under
reactive
conditions
require
their
oxidative
regeneration,
with
the
cycling
between
clusters
cations.
The
intermediate
species
have
remained
only
incompletely
understood.
Here,
we
report
an
experimental
theoretical
investigation
structure,
bonding,
local
environment
cationic
ZSM-5,
which
key
intermediates
this
cycling.
Upon
exposure
to
O2
at
700
°C,
fragmentation
occurs,
Pt2+
ions
stabilized
six-membered
rings
that
contain
paired
aluminum
sites.
When
exposed
CO
mild
conditions,
these
form
highly
uniform
gem-dicarbonyls,
can
be
converted
H2
Ptδ+
monocarbonyls.
This
conversion,
weakens
platinum-zeolite
is
a
first
step
toward
migration
aggregation
into
clusters.
X-ray
absorption
infrared
spectra
provide
evidence
reductive
transformations
various
gas
environments.
chemistry
general,
as
shown
by
observation
gem-dicarbonyls
several
commercially
used
zeolites
(ZSM-5,
Beta,
mordenite,
Y).
The Journal of Physical Chemistry C,
Journal Year:
2022,
Volume and Issue:
126(3), P. 1439 - 1449
Published: Jan. 14, 2022
Pd-ion-exchanged
zeolites
have
emerged
as
promising
materials
for
the
adsorption
and
oxidation
of
air
pollutants.
For
low-temperature
vehicle
exhaust,
dispersed
Pd
ions
can
adsorb
NOx
even
in
H2O-rich
exhaust
containing
carbon
monoxide.
To
understand
this
phenomenon,
changes
ligand
environment
to
be
monitored
situ.
Herein,
we
directly
observe
activation
hydrated
ion
shielded
by
H2O
into
a
carbonyl–nitrosyl
complex
Pd2+(NO)(CO)
SSZ-13
zeolite.
The
subsequent
thermal
desorption
ligands
on
proceeds
nitrosyl
Pd2+
rather
than
carbonyl
under
various
conditions.
Thus,
CO
molecules
act
additional
provide
an
alternative
pathway
with
lower
energy
barrier
accelerating
NO
through
complex.
We
further
demonstrate
that
hydration
zeolite
is
prerequisite
CO-induced
reduction
metallic
Pd.
limited
dry
conditions
at
temperatures
high
500
°C,
while
water
makes
it
possible
near
RT.
However,
primary
sites
are
gases
water.
These
findings
clarify
mechanistic
aspects
passive
(PNA)
process
will
help
extend
chemistry
zeolite-based
adsorbers
practical
applications.
ACS Catalysis,
Journal Year:
2022,
Volume and Issue:
12(20), P. 12809 - 12822
Published: Oct. 7, 2022
The
methane
dry
reforming
(DRM)
reaction
mechanism
was
explored
via
mechanochemically
prepared
Pd/CeO2
catalysts
(PdAcCeO2M),
which
yield
unique
Pd–Ce
interfaces,
where
PdAcCeO2M
has
a
distinct
and
higher
reactivity
for
DRM
relative
to
traditionally
synthesized
impregnated
(PdCeO2IW).
In
situ
characterization
density
functional
theory
calculations
revealed
that
the
enhanced
chemistry
of
can
be
attributed
presence
carbon-modified
Pd0
Ce4+/3+
surface
arrangement,
Pd–CO
intermediate
species
strong
Pd–CeO2
interactions
are
activated
sustained
exclusively
under
conditions.
This
arrangement
leads
highly
selective
pathways
prefer
direct
oxidation
CHx
CO,
identified
on
using
isotope
labeled
diffuse
reflectance
infrared
Fourier
transform
spectroscopy
highlighting
linear
bound
metallic
C-modified
Pd,
leading
adsorbed
HCOO
[1595
cm–1]
as
key
intermediates,
stemming
from
associative
CO2
reduction.
milled
materials
contrast
strikingly
with
processes
observed
IW
samples
(PdCeO2IW)
competing
reverse
water
gas
shift
predominates.
Environmental Science & Technology,
Journal Year:
2024,
Volume and Issue:
58(23), P. 10357 - 10367
Published: May 10, 2024
The
urgent
environmental
concern
of
methane
abatement,
attributed
to
its
high
global
warming
potential,
necessitates
the
development
oxidation
catalysts
(MOC)
with
enhanced
low-temperature
activity
and
durability.
Herein,
an
iridium-doped
PdO