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

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^–1 h^–1 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^–1 h^–1 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

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_<i>x</i> Reduction

A series of new heterobimetallic zeolites has been synthesized by incorporating a secondary metal cation M (Sc³⁺, Fe³⁺, In³⁺, and La³⁺) 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 M³⁺ is hosted in zeolite structures in the vicinity of Cu­(II), resulting in high NO_<i>x</i> conversion activity at 150 °C. Among various zeolites reported here, CuFe-SSZ-13 offers the best NO_<i>x</i> 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⁺ generated by heterobimetallic zeolites is probably responsible for their superior low-temperature NO_<i>x</i> activity

CO Oxidation on Supported Single Pt Atoms: Experimental and ab Initio Density Functional Studies of CO Interaction with Pt Atom on θ‑Al₂O₃(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 (Al₂O₃), 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 O₂ over CO. CO then bonds with the oxygenated Pt atom and forms a carbonate which dissociates to liberate CO₂, 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 CO₃ unless the temperature is raised to eliminate CO₂. We find evidence for CO₃ 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-Al₂O₃ are also presented

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