Abstract:We demonstrate the self-assembly of transition metal carbide nanoparticles coated with atomically-thin noble metal monolayers by carburizing mixtures of noble metal salts and transition metal oxides encapsulated in removable silica templates. This approach allows for control of the final core-shell architecture, including particle size, monolayer coverage, and heterometallic composition. Carbon-supported Ti0.1W0.9C nanoparticles coated with Pt or bimetallic PtRu monolayers exhibited enhanced resistance to sintering and CO poisoning, achieving an order of magnitude increase in specific activity over commercial catalysts for methanol electrooxidation after 10,000 cycles. These core-shell materials provide a new direction to reduce the loading, enhance the activity, and increase the stability of noble metal catalysts. One Sentence Summary:The self-assembly of transition metal carbide nanoparticles coated with atomically-thin noble metal monolayers results in a highly active, stable, and tunable catalytic platform.Noble metal (NM) catalysts critically enable many existing and emerging technologies, such as catalytic converters (1), reforming (2), and fuel cells (3). However, their scarcity and high cost necessitate the development of catalytic systems with reduced NM loadings, increased activity, and improved durability. In this respect, various nanostructured architectures have been investigated, including atomically-dispersed NM catalysts (4), hollow nanocages (5, 6), alloyed nanoparticles (NPs) (7), and core-shell structures (8, 9). In particular, core-shell NPs composed of an earth-abundant core coated with an atomically-thin NM shell are a promising platform that offers both design flexibility and reduced precious metal loadings. However, achieving independent control over the particle size, core composition, shell composition, and shell thickness poses a substantial challenge (8, 9). State-of-the-art synthetic methods are predominantly limited to a few earth-abundant metallic cores (e.g., Fe, Co, Ni, and Cu) that allow for more precise synthetic control; however, these metal cores form intrinsically metastable core-shell particles that restructure during heating (10-12) or electrochemical cycling (13, 14).Early transition metal carbides (TMCs) are earth-abundant ceramics with ideal topochemical properties for supporting precious metal shells (15-17). First, TMCs exhibit metallic electrical conductivity, corrosion resistance, and high melting points (18). Second, precious metals tend to bind strongly to metal-terminated early TMC surfaces (Fig. S1), but cannot readily form stable carbides (19). Thus, NMs should coat TMC surfaces, but should not alloy with the underlying core. In particular, tungsten carbide (WC) is inexpensive (Fig. S2), exhibits a "platinum-like" density of electronic states (20, 21), and its metal-terminated surface forms interfacial Pt-WC bonds that are ca. 90 kJ mol -1 stronger than interfacial Pt-Pt bonds (Fig. S1). Although experimental studies on model thin film systems have co...

Atomic layer deposition (ALD) of an alumina overcoat can stabilize a base metal catalyst (e.g., copper) for liquid-phase catalytic reactions (e.g., hydrogenation of biomass-derived furfural in alcoholic solvents or water), thereby eliminating the deactivation of conventional catalysts by sintering and leaching. This method of catalyst stabilization alleviates the need to employ precious metals (e.g., platinum) in liquid-phase catalytic processing. The alumina overcoat initially covers the catalyst surface completely. By using solid state NMR spectroscopy, X-ray diffraction, and electron microscopy, it was shown that high temperature treatment opens porosity in the overcoat by forming crystallites of γ-Al2 O3 . Infrared spectroscopic measurements and scanning tunneling microscopy studies of trimethylaluminum ALD on copper show that the remarkable stability imparted to the nanoparticles arises from selective armoring of under-coordinated copper atoms on the nanoparticle surface.

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Anthropogenic emissions of CO2 from industrial processes are considered the major cause of global warming and ocean acidification. To this end, different abatement strategies have been sought to capture CO2 directly from various effluent sources. Carbon capture and sequestration (CCS) has been touted to solve this problem; however, due to the challenges associated with this approach, research efforts have been focused on the development of dual-function materials (DFMs) that can effectively capture and convert CO2 to value-added products. In this review, we first describe existent CO2 capture processes, followed by relevant CO2 adsorbents. Then, we focus on the development of DFMs for CO2 capture and conversion through various reaction pathways, such as methanation, reverse water-gas shift, and dry reforming. We also elaborate on the challenges associated with these systems with emphasis on the stability and regenerability of the materials. Finally, some future perspectives and possible areas of study are highlighted.

A combined theoretical and experimental approach is presented that uses a comprehensive mean‐field microkinetic model, reaction kinetics experiments, and scanning transmission electron microscopy imaging to unravel the reaction mechanism and provide insights into the nature of active sites for formic acid (HCOOH) decomposition on Au/SiC catalysts. All input parameters for the microkinetic model are derived from periodic, self‐consistent, generalized gradient approximation (GGA‐PW91) density functional theory calculations on the Au(111), Au(100), and Au(211) surfaces and are subsequently adjusted to describe the experimental HCOOH decomposition rate and selectivity data. It is shown that the HCOOH decomposition follows the formate (HCOO) mediated path, with 100% selectivity toward the dehydrogenation products (CO2 + H2) under all reaction conditions. An analysis of the kinetic parameters suggests that an Au surface in which the coordination number of surface Au atoms is ≤4 may provide a better model for the active site of HCOOH decomposition on these specific supported Au catalysts. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1303–1319, 2014

a b s t r a c tHigh-temperature calcination and reduction treatments of cobalt particles (17-20 nm) supported on TiO 2 create cobalt particles covered with a TiO y layer. The layer thickness ranges from 2.8 to 4.0 nm. These phenomena, commonly called strong metal-support interaction (SMSI), can be used to improve the catalyst stability and change the catalyst selectivity. For example, non-overcoated cobalt catalysts leached during aqueous-phase hydrogenation (APH) of furfuryl alcohol, losing 44.6% of the cobalt after 35 h time-on-stream. In contrast, TiO y -overcoated cobalt catalysts did not lose any measurable cobalt by leaching and the cobalt particle size remained constant after 105 h time-on-stream. The 1,5-pentanediol selectivity from furfuryl alcohol hydrogenolysis increased with increasing TiO y layer thickness. The stabilized cobalt catalyst also had high yields for APH of xylose to xylitol (99%) and APH of furfural to furfuryl alcohol (95%). These results show that the SMSI effect produces a catalyst with a similar structure as catalysts prepared by atomic layer deposition, thereby opening up a cheaper and more industrially relevant method of stabilizing base-metal catalysts for aqueous-phase biomass conversion reactions. In addition, the SMSI effect can be used to tune catalyst selectivity, thus allowing the more precise atomic scale design of supported metal catalysts.

One of the most significant challenges in the use of heterogeneous catalysts is the loss of activity and/or selectivity with time on stream, and researchers have explored different methods to overcome this problem. Recently, the coating of catalysts to control their deactivation has generated much research traction. This Review is aimed at studying different encapsulation techniques employed for controlling catalyst deactivation. Focus is given to the prevention of irreversible modes of deactivation, such as sintering and leaching. In this Review, we elaborate on different entrapment methods used to protect catalysts from deactivation in both liquid and gas reaction media. Relevant probe reactions are discussed with emphasis on the catalyst activity and stability. Challenges associated with those processes are also described with emphasis on the mass transfer limitations as a result of the coverage of the active sites. Finally, some future perspectives and areas for possible improvement are highlighted.

Background: Right ventricular failure (RVF) is a cause of major morbidity and mortality after left ventricular assist device (LVAD) implantation. It is, therefore, integral to identify patients who may benefit from biventricular support early post-LVAD implantation. Our objective was to explore the performance of risk prediction models for RVF in adult patients undergoing LVAD implantation. Methods: A systematic search was performed on Medline, Embase, Cochrane Central Register of Controlled Trials, and Cochrane Database of Systematic Reviews from inception until August 2019 for all relevant studies. Performance was assessed by discrimination (via C statistic) and calibration if reported. Study quality was assessed using the Prediction Model Risk of Bias Assessment Tool criteria. Results: After reviewing 3878 citations, 25 studies were included, featuring 20 distinctly derived models. Five models were derived from large multicenter cohorts: the European Registry for Patients With Mechanical Circulatory Support, Interagency Registry for Mechanically Assisted Circulatory Support, Kormos, Pittsburgh Bayesian, and Mechanical Circulatory Support Research Network RVF models. Seventeen studies (68%) were conducted in cohorts implanted with continuous-flow LVADs exclusively. The definition of RVF as an outcome was heterogenous among models. Seven derived models (28%) were validated in at least 2 cohorts, reporting limited discrimination (C-statistic range, 0.53–0.65). Calibration was reported in only 3 studies and was variable. Conclusions: Existing RVF prediction models exhibit heterogeneous derivation and validation methodologies, varying definitions of RVF, and are mostly derived from single centers. Validation studies of these prediction models demonstrate poor-to-modest discrimination. Newer models are derived in cohorts implanted with continuous-flow LVADs exclusively and exhibit modest discrimination. Derivation of enhanced discriminatory models and their validations in multicenter cohorts is needed.