High temperature electrochemical energy conversion and storage technologies, such as solid oxide electrochemical cells (SOCs), have emerged as promising alternatives to mitigate environmental issues ...associated with combustion-based technologies. There has been increased interest for nanoengineering SOC electrodes to enhance their efficiency. A major drive is the necessity for improved electrode kinetics via optimization of electrocatalysts for different key reactions in these devices. In this perspective, we discuss the requirements for SOC electrodes and nanoengineering strategies employed to achieve flexibility in electrode materials. We focus on identifying ways in which these nanoengineered materials foster advancements in the SOC electrocatalytic activity, selectivity, and stability. We conclude by proposing approaches that would lead to more stable electrocatalytic nanostructures with high degree of control over the number and nature of active sites. These nanostructures would enable systematic kinetic studies that could provide an in depth understanding of the reaction mechanisms that govern performance, leading to valuable knowledge for designing optimal electrode materials.
Conversion of carbohydrates to 5-(hydroxymethyl)furfural (HMF) may provide a step forward toward achieving a renewable biomass-based chemicals and fuels platform. Recently, we reported that a ...tin-containing, high-silica molecular sieve with the zeolite beta topology (Sn-Beta) can efficiently catalyze the isomerization of glucose to fructose in aqueous media at low pH. Herein, we describe the combination of Sn-Beta with acid catalysts in a one vessel, biphasic reactor system to synthesize HMF from carbohydrates such as glucose, cellobiose, and starch with high efficiency. HMF selectivities over 70% were obtained using this “one-pot” biphasic water/tetrahydrofuran (THF) reactor system. The key to successfully achieving the conversions/selectivities reported is that Sn-Beta is able to convert glucose to fructose at pH near 1 and in saturated aqueous salt solutions.
Abstract
Atmospheric NO
2
is of great concern due to its adverse effects on human health and the environment, motivating research on NO
2
detection and remediation. Existing low-cost room-temperature ...NO
2
sensors often suffer from low sensitivity at the ppb level or long recovery times, reflecting the trade-off between sensor response and recovery time. Here, we report an atomically dispersed metal ion strategy to address it. We discover that bimetallic PbCdSe quantum dot (QD) gels containing atomically dispersed Pb ionic sites achieve the optimal combination of strong sensor response and fast recovery, leading to a high-performance room-temperature p-type semiconductor NO
2
sensor as characterized by a combination of ultra–low limit of detection, high sensitivity and stability, fast response and recovery. With the help of theoretical calculations, we reveal the high performance of the PbCdSe QD gel arises from the unique tuning effects of Pb ionic sites on NO
2
binding at their neighboring Cd sites.
There has been a recent surge of interest in multicomponent catalysts that combine properties of chemically diverse materials. A major factor in this increased interest is the widespread recognition ...that the scaling relationships for adsorption and transition state energies of reactions place significant constraints on making step-change improvements in catalyst performance using monofunctional catalysts. In this perspective, we review the fundamental rationale for multicomponent materials and describe several classes of materials that offer promise for improving activity and selectivity in catalysis. Our focus is on illustrating how recent advances in the ability to prepare precisely controlled multicomponent nanostructures have the potential to enhance the capability to design highly active and selective catalysts.
We report the results of detailed kinetic studies for methane steam reforming on supported Ni and Sn/Ni surface alloy catalysts. The kinetic data were interpreted in terms of mechanism-based overall ...rate expression. We show that the activation of C
H bonds in methane is the rate-controlling step on both catalysts. Isotopic CH
4/CD
4 labeling studies were performed to independently verify the proposed mechanism. The role of Sn is to displace Ni atoms from under-coordinated sites on Ni particles and to move the critical reaction channels to more abundant well-coordinated sites. We show that previously observed increased resistance to carbon deactivation of Sn/Ni compared to monometallic Ni in hydrocarbon reforming reactions can be attributed to the Sn-induced lowering in the binding energy of carbon on low-coordinate sites, which serve as carbon nucleation centers, and to an enhanced propensity of Sn/Ni to oxidize carbon surface species. The conclusions derived from the experimental studies are in agreement with DFT calculations.
Sn atoms dispersed on supported Ni catalysts alter catalytic methane steam reforming by (i) changing the nature of the active sites, (ii) increasing the overall activation barrier, and (iii) improving the catalyst tolerance to carbon-induced deactivation.
Significant emphasis has been placed recently in engineering the catalytic environment beyond the active site for tuning the activity, selectivity, and stability of supported metal catalysts for ...targeted reactions. The environment around the active site in supported catalysts can be modified by introducing multi-dimensionality through alloying, encapsulation, and surface bound ligands. In this Review, we provide a summary of synthesis strategies that have enabled the design of multifunctionality and multidimensionality in heterogeneous supported catalysts. We specifically discuss alloys, encapsulated/inverted catalytic structures, and ligand capped metal nanoparticle systems. We highlight the effects on catalyst activity, selectivity and stability that arise from modifying the neighboring two-dimensional environment through alloying or three-dimensional environment through encapsulation with porous inorganic films or surface organic moieties. We conclude by providing a short perspective on the promises and remaining challenges associated with engineering the local environment around the active sites of supported heterogeneous catalysts.
Isomerization of sugars is used in a variety of industrially relevant processes and in glycolysis. Here, we show that hydrophobic zeolite beta with framework tin or titanium Lewis acid centers ...isomerizes sugars, e.g., glucose, via reaction pathways that are analogous to those of metalloenzymes. Specifically, experimental and theoretical investigations reveal that glucose partitions into the zeolite in the pyranose form, ring opens to the acyclic form in the presence of the Lewis acid center, isomerizes into the acyclic form of fructose, and finally ring closes to yield the furanose product. The zeolite catalysts provide processing advantages over metalloenzymes such as an ability to work at higher temperatures and in acidic conditions that allow for the isomerization reaction to be coupled with other important conversions.
Steam reforming is a process where a hydrocarbon is converted into hydrogen and oxygenated carbon species. Ni is often used as catalyst for the reaction. Long term stability of steam reforming ...catalysts is governed by their ability to selectively oxidize C atoms while preventing C−C bond formation. In this communication we demonstrate that C atom chemistry over Ni surfaces can be controlled by surface alloying. We show that bimetallic Sn/Ni catalyst is much more carbon-tolerant that monometallic Ni. The main reason for this is that Sn alloying results in dramatically lower rates of C−C bond formation as compared to C-oxidation. The bimetallic catalyst was identified in quantum computational studies of the underlying atomic-scale phenomena that govern C atom surface chemistry. The catalysts were also characterized with various electron- and X-ray-based microscopies and spectroscopies.
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