12 research outputs found
Cu-ZSM-5 catalyzed low-temperature hydrogen peroxide-induced methane-to-methanol conversion
We report herein that Cu-ZSM-5 is an effective catalyst for methane oxidation with hydrogen peroxide, provided Cu-ZSM-5 is synthesized by ion exchange. The reaction conditions for efficient conversion of methane to methanol over Cu-ZSM-5 are also reported
Materials Chemistry Issues Related to Advanced Materials Applications in the Automotive Industry
Catalytic Conversion of Biomass-Derived Ethanol to Liquid Hydrocarbon Blendstock: Effect of Light Gas Recirculation
We
describe a light gas recirculation (LGR) method to increase
the liquid hydrocarbon yield with a reduced aromatic content from
catalytic conversion of ethanol to hydrocarbons. The previous liquid
hydrocarbon yield is ∼40% from one-pass ethanol conversion
over the V-ZSM-5 catalyst at 350 °C and atmospheric pressure,
where the remaining ∼60% yield is light gas hydrocarbons. In
comparison, the liquid hydrocarbon yield increases to 80% when a simulated
light gas hydrocarbon stream is co-fed at a rate of 0.053 mol g<sup>–1</sup> h<sup>–1</sup> with ethanol as a result of
the conversion of most of the light olefins. The LGR also significantly
improves the quality of the liquid hydrocarbon blendstock by reducing
the aromatic content and overall benzene concentration. For 0.027
mol g<sup>–1</sup> h<sup>–1</sup> light gas mixture
co-feeding, the average aromatic content in liquid hydrocarbons is
51.5% compared to 62.5% aromatic content in the ethanol only experiment.
The average benzene concentration decreases from 3.75 to 1.5%, which
is highly desirable because the United States Environmental Protection
Agency (U.S. EPA) limits the benzene concentration in gasoline to
0.62%. As a result of a low benzene concentration, the blend wall
for ethanol-derived liquid hydrocarbons changes from ∼18 to
43%. The remaining light paraffins and olefins can be further converted
to valuable benzene, toluene, and xylenes (BTX) products (94% BTX
in the liquid) over Ga-ZSM-5 at 500 °C. Thus, the LGR is an effective
approach to convert ethanol to liquid hydrocarbons with a higher liquid
yield and low aromatic content, especially a low benzene concentration,
which could be blended with gasoline in a much higher ratio than ethanol
or ethanol-derived hydrocarbon blendstock
Synthesis of boron nitride ceramics from oligomeric precursors derived from 2-(dimethylamino)-4,6-dichloroborazine
A Pathway for the Growth of Core–Shell Pt–Pd Nanoparticles
The aging of both Pt–Pd nanoparticles
and core–shell
Pt–Pd nanoparticles has been reported to result in alloying
of Pt with Pd. In comparison to monometallic Pt catalysts, the growth
of Pd–Pt bimetallics is slower; however, the mechanism of growth
of particles and the mechanism by which Pd improves the hydrothermal
durability of bimetallic Pd–Pt particles remains uncertain.
In our work on hydrothermal aging of core–shell Pt–Pd
nanoparticles, synthesized by solution methods, with varying Pd:Pt
ratio of 1:4, 1:1, and 4:1, we compare the growth of core–shell
Pt–Pd nanoparticles and find that particles grow by migrating
and joining together. The unique feature of the observed growth is
that Pd shells from both particles open up and join, thereby allowing
the cores to merge. At high temperatures, alloying occurs in good
agreement with reports by other workers
Heterometal Incorporation in Metal-Exchanged Zeolites Enables Low-Temperature Catalytic Activity of NO<sub><i>x</i></sub> Reduction
A series of new heterobimetallic zeolites has been synthesized
by incorporating a secondary metal cation M (Sc<sup>3+</sup>, Fe<sup>3+</sup>, In<sup>3+</sup>, and La<sup>3+</sup>) in Cu-exchanged ZSM-5,
zeolite-β, and SSZ-13 zeolites under carefully controlled experimental
conditions. Characterization by diffuse-reflectance ultraviolet–visible
spectroscopy (UV–vis), X-ray powder diffraction (XRD), extended
X-ray absorption fine structure spectroscopy (EXAFS), and electron
paramagnetic resonance spectroscopy (EPR) does not permit conclusive
structural determination but supports the proposal that M<sup>3+</sup> is hosted in zeolite structures in the vicinity of CuÂ(II), resulting
in high NO<sub><i>x</i></sub> conversion activity at 150
°C. Among various zeolites reported here, CuFe-SSZ-13 offers
the best NO<sub><i>x</i></sub> conversion activity in the
150–650 °C range and is hydrothermally stable when tested
under accelerated aging conditions. Mechanistic studies employing
stopped-flow diffuse reflectance FT-IR spectroscopy (DRIFTS) suggest
that the high concentration of NO<sup>+</sup> generated by heterobimetallic
zeolites is probably responsible for their superior low-temperature
NO<sub><i>x</i></sub> activity
CO Oxidation on Supported Single Pt Atoms: Experimental and ab Initio Density Functional Studies of CO Interaction with Pt Atom on θ‑Al<sub>2</sub>O<sub>3</sub>(010) Surface
Although there are
only a few known examples of supported single-atom
catalysts, they are unique because they bridge the gap between homogeneous
and heterogeneous catalysis. Here, we report the CO oxidation activity
of monodisperse single Pt atoms supported on an inert substrate, θ-alumina
(Al<sub>2</sub>O<sub>3</sub>), in the presence of stoichiometric oxygen.
Since CO oxidation on single Pt atoms cannot occur via a conventional
Langmuir–Hinshelwood scheme (L–H scheme) which requires
at least one Pt–Pt bond, we carried out a first-principles
density functional theoretical study of a proposed pathway which is
a variation on the conventional L–H scheme and inspired by
the organometallic chemistry of platinum. We find that a single supported
Pt atom prefers to bond to O<sub>2</sub> over CO. CO then bonds with
the oxygenated Pt atom and forms a carbonate which dissociates to
liberate CO<sub>2</sub>, leaving an oxygen atom on Pt. Subsequent
reaction with another CO molecule regenerates the single-atom catalyst.
The energetics of the proposed mechanism suggests that the single
Pt atoms will get covered with CO<sub>3</sub> unless the temperature
is raised to eliminate CO<sub>2</sub>. We find evidence for CO<sub>3</sub> coverage at room temperature supporting the proposed mechanism
in an in situ diffuse reflectance infrared study of CO adsorption
on the catalyst’s supported single atoms. Thus, our results
clearly show that supported Pt single atoms are catalytically active
and that this catalytic activity can occur without involving the substrate.
Characterization by electron microscopy and X-ray absorption studies
of the monodisperse Pt/θ-Al<sub>2</sub>O<sub>3</sub> are also
presented
Ab Initio Density Functional Calculations of Adsorption of Transition Metal Atoms on θ-Al 2
Tumour exosomal CEMIP protein promotes cancer cell colonization in brain metastasis
The development of effective therapies against brain metastasis is currently hindered by limitations in our understanding of the molecular mechanisms driving it. Here we define the contributions of tumour-secreted exosomes to brain metastatic colonization and demonstrate that pre-conditioning the brain microenvironment with exosomes from brain metastatic cells enhances cancer cell outgrowth. Proteomic analysis identified cell migration-inducing and hyaluronan-binding protein (CEMIP) as elevated in exosomes from brain metastatic but not lung or bone metastatic cells. CEMIP depletion in tumour cells impaired brain metastasis, disrupting invasion and tumour cell association with the brain vasculature, phenotypes rescued by pre-conditioning the brain microenvironment with CEMIP exosomes. Moreover, uptake of CEMIP+ exosomes by brain endothelial and microglial cells induced endothelial cell branching and inflammation in the perivascular niche by upregulating the pro-inflammatory cytokines encoded by Ptgs2, Tnf and Ccl/Cxcl, known to promote brain vascular remodelling and metastasis. CEMIP was elevated in tumour tissues and exosomes from patients with brain metastasis and predicted brain metastasis progression and patient survival. Collectively, our findings suggest that targeting exosomal CEMIP could constitute a future avenue for the prevention and treatment of brain metastasis