Quantifying the Hydration-Dependent Dynamics of Cu Migration and Activity in Zeolite Omega for the Partial Oxidation of Methane.

Copper-exchanged zeolite omega (Cu-omega) is a potent material for the selective conversion of methane-to-methanol (MtM) via the oxygen looping approach. However, its performance exhibits substantial variation depending on the operational conditions. Under an isothermal temperature regime, Cu-omega demonstrates subdued activity below 230 °C, but experiences a remarkable increase in activity at 290 °C.

Colloidal Atomic Layer Deposition on Nanocrystals Using Ligand-Modified Precursors.

Atomic layer deposition (ALD) is a method to grow thin metal oxide layers on a variety of materials for applications spanning from electronics to catalysis. Extending ALD to colloidally stable nanocrystals promises to combine the benefits of thin metal oxide coatings with the solution processability of the nanocrystals. However, challenges persist in applying this method, which relate to finding precursors that promote the growth of the metal oxide while preserving colloidal stability throughout the process.

The Enigma of Methanol Synthesis by Cu/ZnO/AlO-Based Catalysts.

The activity and durability of the Cu/ZnO/AlO (CZA) catalyst formulation for methanol synthesis from CO/CO/H feeds far exceed the sum of its individual components. As such, this ternary catalytic system is a prime example of synergy in catalysis, one that has been employed for the large scale commercial production of methanol since its inception in the mid 1960s with precious little alteration to its original formulation. Methanol is a key building block of the chemical industry.

Hybrid oxide coatings generate stable Cu catalysts for CO electroreduction.

Hybrid organic/inorganic materials have contributed to solve important challenges in different areas of science. One of the biggest challenges for a more sustainable society is to have active and stable catalysts that enable the transition from fossil fuel to renewable feedstocks, reduce energy consumption and minimize the environmental footprint. Here we synthesize novel hybrid materials where an amorphous oxide coating with embedded organic ligands surrounds metallic nanocrystals.

Surface Chemistry Dictates the Enhancement of Luminescence and Stability of InP QDs upon c-ALD ZnO Hybrid Shell Growth.

Indium phosphide quantum dots (InP QDs) are a promising example of Restriction of Hazardous Substances directive (RoHS)-compliant light-emitting materials. However, they suffer from low quantum yield and instability upon processing under ambient conditions. Colloidal atomic layer deposition (c-ALD) has been recently proposed as a methodology to grow hybrid materials including QDs and organic/inorganic oxide shells, which possess new functions compared to those of the as-synthesized QDs.

Assessing the Productivity of the Direct Conversion of Methane-to-Methanol over Copper-Exchanged Zeolite Omega (MAZ) via Oxygen Looping.

The methane-to-methanol (MtM) conversion via the oxygen looping approach using copper-exchanged zeolites has been extensively studied over the last decade. While a lot of research has focussed on maximizing yield and selectivity, little has been directed toward productivity-a metric far more meaningful for evaluating industrial potential. Using copper-exchanged zeolite omega (Cu-omega), a material highly active and selective for the MtM conversion using the isothermal oxygen looping approach, we show that this material exhibits unprecedented potential for industrial valorization.

Alloying as a Strategy to Boost the Stability of Copper Nanocatalysts during the Electrochemical CO Reduction Reaction.

Copper nanocatalysts are among the most promising candidates to drive the electrochemical CO reduction reaction (CORR). However, the stability of such catalysts during operation is sub-optimal, and improving this aspect of catalyst behavior remains a challenge. Here, we synthesize well-defined and tunable CuGa nanoparticles (NPs) and demonstrate that alloying Cu with Ga considerably improves the stability of the nanocatalysts.

Copper-exchanged large-port and small-port mordenite (MOR) for methane-to-methanol conversion.

Zeolite mordenite (MOR) is one of the most studied zeolites for the stepwise direct conversion of methane to methanol, but it also can exist in two forms: large port and small port. Here we report that the synthesis and selection of the parent mordenite is critical for optimizing productivity, and that large-port mordenite outperforms small-port mordenite for the stepwise conversion of methane to methanol.

Drastic Events and Gradual Change Define the Structure of an Active Copper-Zinc-Alumina Catalyst for Methanol Synthesis.

The copper-zinc-alumina (CZA) catalyst is one of the most important catalysts. Nevertheless, understanding of the complex CZA structure is still limited and hampers further optimization. Critical to the production of a highly active and stable catalyst are optimal start-up procedures in hydrogen.

A multimodal analytical toolkit to resolve correlated reaction pathways: the case of nanoparticle formation in zeolites.

Unraveling the complex, competing pathways that can govern reactions in multicomponent systems is an experimental and technical challenge. We outline and apply a novel analytical toolkit that fully leverages the synchronicity of multimodal experiments to deconvolute causal from correlative relationships and resolve structural and chemical changes in complex materials. Here, simultaneous multimodal measurements combined diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and angular dispersive X-ray scattering suitable for pair distribution function (PDF), X-ray diffraction (XRD) and small angle X-ray scattering (SAXS) analyses.

In Situ X-ray Absorption Spectroscopy and Droplet-Based Microfluidics: An Analysis of Calcium Carbonate Precipitation.

Droplet-based microfluidic systems are ideally suited for the investigation of nucleation and crystallization processes. To best leverage the features of such platforms (including exquisite time resolution and high-throughput operation), sensitive and in situ detection schemes are needed to extract real-time chemical information about all species of interest. In this regard, the extension of conventional (UV, visible, and infrared) optical detection schemes to the X-ray region of the electromagnetic spectrum is of high current interest, as techniques such as X-ray absorption spectroscopy (XAS) provide for the element-specific investigation of the local chemical environment.

Structure of copper sites in zeolites examined by Fourier and wavelet transform analysis of EXAFS.

Copper-exchanged zeolites are a class of redox-active materials that find application in the selective catalytic reduction of exhaust gases of diesel vehicles and, more recently, the selective oxidation of methane to methanol. However, the structure of the active copper-oxo species present in zeolites under oxidative environments is still a subject of debate. Herein, we make a comprehensive study of copper species in copper-exchanged zeolites with MOR, MFI, BEA, and FAU frameworks and for different Si/Al ratios and copper loadings using X-ray absorption spectroscopy.

Heterogeneously Catalyzed Aerobic Oxidation of Methane to a Methyl Derivative.

A promising strategy to break through the selectivity-conversion limit of direct methane conversion to achieve high yields is the protection of methanol via esterification to a more stable methyl ester. We present an aerobic methane-to-methyl-ester approach that utilizes a highly dispersed, cobalt-containing solid catalyst, along with significantly more favorable reaction conditions compared to existing homogeneously-catalyzed approaches (e.g.

Mechanistic Study of Carbon Dioxide Hydrogenation over Pd/ZnO-Based Catalysts: The Role of Palladium-Zinc Alloy in Selective Methanol Synthesis.

Pd/ZnO catalysts show good activity and high selectivity to methanol during catalytic CO hydrogenation. The Pd-Zn alloy phase has usually been considered as the active phase, though mechanistic studies under operando conditions have not been conducted to verify this. Here, we report a mechanistic study under realistic conditions of methanol synthesis, using in situ and operando X-ray absorption spectroscopy, X-ray powder diffraction, and time-resolved isotope labeling experiments coupled with FTIR spectroscopy and mass spectrometry.

Titanium-Anchored Gold on Silica for Enhanced Catalytic Activity in Aqueous Ethanol Oxidation.

The heterogeneously catalyzed oxidation of bioethanol offers a promising route to bio-based acetic acid. Here, we assess an alternative method to support gold nanoparticles, which aims to improve selectivity to acetic acid through minimizing over-oxidation to carbon dioxide. The most promising support system is 5 wt % titanium on silica, which combines the high surface area of silica with the stabilizing effect of titania on the gold particles.

The unique interplay between copper and zinc during catalytic carbon dioxide hydrogenation to methanol.

In spite of numerous works in the field of chemical valorization of carbon dioxide into methanol, the nature of high activity of Cu/ZnO catalysts, including the reaction mechanism and the structure of the catalyst active site, remains the subject of intensive debate. By using high-pressure operando techniques: steady-state isotope transient kinetic analysis coupled with infrared spectroscopy, together with time-resolved X-ray absorption spectroscopy and X-ray powder diffraction, and supported by electron microscopy and theoretical modeling, we present direct evidence that zinc formate is the principal observable reactive intermediate, which in the presence of hydrogen converts into methanol. Our results indicate that the copper-zinc alloy undergoes oxidation under reaction conditions into zinc formate, zinc oxide and metallic copper.

Molecular Approach to Generate Cu(II) Sites on Silica for the Selective Partial Oxidation of Methane.

The selective partial oxidation of methane to methanol remains a great challenge in the field of catalysis. Cu-exchanged zeolites are promising materials, directly and selectively converting methane to methanol with high yield under cyclic conditions. However, the economic viability of these aluminosilicate materials for potential industrial applications remains a challenge.

Unwanted effects of X-rays in surface grafted copper(ii) organometallics and copper exchanged zeolites, how they manifest, and what can be done about them.

Copper(ii) containing materials are widely studied for a very diverse array of applications from biology, through catalysis, to many other materials chemistry based applications. We show that, for grafted copper compounds at the surface of silica, and for the study of the selective conversion of methane to methanol using copper ion-exchanged zeolites, the application of focused X-ray beams for spectroscopic investigations is subject to significant challenges. We demonstrate how unwanted effects due to the X-rays manifest, which can prevent the study of certain types of reactive systems, and/or lead to the derivation of results that are not at all representative of the behavior of the materials in question.

Non-oxidative Methane Coupling over Silica versus Silica-Supported Iron(II) Single Sites.

Non-oxidative CH coupling is promoted by silica with incorporated iron sites, but the role of these sites and their speciation under reaction conditions are poorly understood. Here, silica-supported iron(II) single sites, prepared via surface organometallic chemistry and stable at 1020 °C in vacuum, are shown to rapidly initiate CH coupling at 1000 °C, leading to 15-22 % hydrocarbons selectivity at 3-4 % conversion. During this process, iron reduces and forms carburized iron(0) nanoparticles.

Active sites and mechanisms in the direct conversion of methane to methanol using Cu in zeolitic hosts: a critical examination.

In this critical review we examine the current state of our knowledge in respect of the nature of the active sites in copper containing zeolites for the selective conversion of methane to methanol. We consider the varied experimental evidence arising from the application of X-ray diffraction, and vibrational, electronic, and X-ray spectroscopies that exist, along with the results of theory. We aim to establish both what is known regarding these elusive materials and how they function, and also where gaps in our knowledge still exist, and offer suggestions and strategies as to how these might be closed such that the rational design of more effective and efficient materials of this type for the selective conversion of methane might proceed further.

Comparative performance of Cu-zeolites in the isothermal conversion of methane to methanol.

The isothermal, low-temperature stepwise conversion of methane to methanol over copper-exchanged zeolites eliminates the time-consuming heating and cooling steps of the conventional high temperature activation approach. To better understand differences between the two approaches, a series of zeolites were screened, of which omega zeolite (MAZ) showed superior performance in both the isothermal and conventional approaches.

Monomeric Copper(II) Sites Supported on Alumina Selectively Convert Methane to Methanol.

Monomeric Cu sites supported on alumina, prepared using surface organometallic chemistry, convert CH to CH OH selectively. This reaction takes place by formation of CH O surface species with the concomitant reduction of two monomeric Cu sites to Cu , according to mass balance analysis, infrared, solid-state nuclear magnetic resonance, X-ray absorption, and electron paramagnetic resonance spectroscopy studies. This material contains a significant fraction of Cu active sites (22 %) and displays a selectivity for CH OH exceeding 83 %, based on the number of electrons involved in the transformation.

On the Mechanism Underlying the Direct Conversion of Methane to Methanol by Copper Hosted in Zeolites; Braiding Cu K-Edge XANES and Reactivity Studies.

The application and quantification of in situ copper K-edge X-ray absorption near-edge structure (XANES), when linked to independently made reactor-based studies of methanol production, result in a majority relation between the production of Cu and methanol from methane that complies with the expectations of a two-electron mechanism founded upon Cu/Cu redox couples.

Solvent-dependent nuclearity, geometry and catalytic activity of [(SPhos)Pd(Ph)Cl].

The nuclearity and structures of the palladium complex [(SPhos)Pd(Ph)Cl] in the solid and solution states are revisited using a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, NMR spectroscopy, mass spectrometry, DFT calculations and trapping experiments. The complex was tested for its catalytic activity in the coupling reaction between chlorobenzene and n-hexylamine, where different deactivation behaviours were observed in toluene, 1,4-dioxane and DMF.