Active sites and structure–activity relationships for methanol synthesis from a stoichiometric mixture of CO2 and H2 were investigated for a series of coprecipitated Cu-based catalysts with temperature-programmed reduction (TPR), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N2O decomposition. Experiments in a reaction chamber attached to an XPS instrument show that metallic Cu exists on the surface of both reduced and spent catalysts and there is no evidence of monovalent Cu+ species. This finding provides reassurance regarding the active oxidation state of Cu in methanol synthesis catalysts because it is observed with 6 compositions possessing different metal oxide additives, Cu particle sizes, and varying degrees of ZnO crystallinity. Smaller Cu particles demonstrate larger turnover frequencies (TOF) for methanol formation, confirming the structure sensitivity of this reaction. No correlation between TOF and lattice strain in Cu crystallites is observed suggesting this structural parameter is not responsible for the activity. Moreover, changes in the observed rates may be ascribed to relative distribution of different Cu facets as more open and low-index surfaces are present on the catalysts containing small Cu particles and amorphous or well-dispersed ZnO. In general, the activity of these systems results from large Cu surface area, high Cu dispersion, and synergistic interactions between Cu and metal oxide support components, illustrating that these are key parameters for developing fundamental mechanistic insight into the performance of Cu-based methanol synthesis catalysts.

Over the past few decades, optical fibers have been widely deployed to implement various applications in high-speed long-distance telecommunication, optical imaging, ultrafast lasers, and optical sensors. Distributed optical fiber sensors characterized by spatially resolved measurements along a single continuous strand of optical fiber have undergone significant improvements in underlying technologies and application scenarios, representing the highest state of the art in optical sensing. This work is focused on a review of three types of distributed optical fiber sensors which are based on Rayleigh, Brillouin, and Raman scattering, and use various demodulation schemes, including optical time-domain reflectometry, optical frequency-domain reflectometry, and related schemes. Recent developments of various distributed optical fiber sensors to provide simultaneous measurements of multiple parameters are analyzed based on their sensing performance, revealing an inherent trade-off between performance parameters such as sensing range, spatial resolution, and sensing resolution. This review highlights the latest progress in distributed optical fiber sensors with an emphasis on energy applications such as energy infrastructure monitoring, power generation system monitoring, oil and gas pipeline monitoring, and geothermal process monitoring. This review aims to clarify challenges and limitations of distributed optical fiber sensors with the goal of providing a pathway to push the limits in distributed optical fiber sensing for practical applications.

The catalytic conversion of CO2 into industrially relevant chemicals is one strategy for mitigating greenhouse gas emissions. Along these lines, electrochemical CO2 conversion technologies are attractive because they can operate with high reaction rates at ambient conditions. However, electrochemical systems require electricity, and CO2 conversion processes must integrate with carbon-free, renewable-energy sources to be viable on larger scales. We utilize Au25 nanoclusters as renewably powered CO2 conversion electrocatalysts with CO2 → CO reaction rates between 400 and 800 L of CO2 per gram of catalytic metal per hour and product selectivities between 80 and 95%. These performance metrics correspond to conversion rates approaching 0.8-1.6 kg of CO2 per gram of catalytic metal per hour. We also present data showing CO2 conversion rates and product selectivity strongly depend on catalyst loading. Optimized systems demonstrate stable operation and reaction turnover numbers (TONs) approaching 6 × 10(6) molCO2 molcatalyst(-1) during a multiday (36 h total hours) CO2 electrolysis experiment containing multiple start/stop cycles. TONs between 1 × 10(6) and 4 × 10(6) molCO2 molcatalyst(-1) were obtained when our system was powered by consumer-grade renewable-energy sources. Daytime photovoltaic-powered CO2 conversion was demonstrated for 12 h and we mimicked low-light or nighttime operation for 24 h with a solar-rechargeable battery. This proof-of-principle study provides some of the initial performance data necessary for assessing the scalability and technical viability of electrochemical CO2 conversion technologies. Specifically, we show the following: (1) all electrochemical CO2 conversion systems will produce a net increase in CO2 emissions if they do not integrate with renewable-energy sources, (2) catalyst loading vs activity trends can be used to tune process rates and product distributions, and (3) state-of-the-art renewable-energy technologies are sufficient to power larger-scale, tonne per day CO2 conversion systems.

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Plasmonic excitation of Au nanoparticles attached to the surface of ZnO catalysts using low power 532 nm laser illumination leads to significant heating of the catalyst and the conversion of CO2 and H2 reactants to CH4 and CO products. Temperature-calibrated Raman spectra of ZnO phonons show that intensity-dependent plasmonic excitation can controllably heat Au-ZnO from 30 to ~600 °C and simultaneously tune the CH4 : CO product ratio. The laser induced heating and resulting CH4 : CO product distribution agrees well with predictions from thermodynamic models and temperature-programmed reaction experiments indicating that the reaction is a thermally driven process resulting from the plasmonic heating of the Au-ZnO. The apparent quantum yield for CO2 conversion under continuous wave (cw) 532 nm laser illumination is 0.030%. The Au-ZnO catalysts are robust and remain active after repeated laser exposure and cycling. The light intensity required to initiate CO2 reduction is low (~2.5 × 10(5) W m(-2)) and achievable with solar concentrators. Our results illustrate the viability of plasmonic heating approaches for CO2 utilization and other practical thermal catalytic applications.

Surface acoustic wave (SAW) technology provides a sensitive platform for sensing chemicals in gaseous and fluidic states with the inherent advantages of passive and wireless operation. In this review, we provide a general overview on the fundamental aspects and some major advances of Rayleigh wave-based SAW sensors in sensing chemicals in a gaseous phase. In particular, we review the progress in general understanding of the SAW chemical sensing mechanism, optimization of the sensor characteristics, and the development of the sensors operational at different conditions. Based on previous publications, we suggest some appropriate sensing approaches for particular applications and identify new opportunities and needs for additional research in this area moving into the future.

Integration of optical fiber with sensitive thin films offers great potential for the realization of novel chemical sensing platforms. In this study, we present a simple design strategy and high performance of nanoporous metal-organic framework (MOF) based optical gas sensors, which enables detection of a wide range of concentrations of small molecules based upon extremely small differences in refractive indices as a function of analyte adsorption within the MOF framework. Thin and compact MOF films can be uniformly formed and tightly bound on the surface of etched optical fiber through a simple solution method which is critical for manufacturability of MOF-based sensor devices. The resulting sensors show high sensitivity/selectivity to CO gas relative to other small gases (H, N, O, and CO) with rapid (

The photocatalytic reduction of CO 2 to value-added chemicals, such as CH 4 , is a promising carbon management approach which can generate revenue from chemical sales to offset the cost of implementing CO 2 capture technologies. To make photocatalytic conversion approaches efficient, economically practical, and industrially scalable, catalysts capable of utilizing visible and near infrared (IR) photons need to be developed. Here we investigate the sensitization of TiO 2 catalysts using PbS quantum dots (QDs) which lead to the size dependent photocatalytic reduction of CO 2 at frequencies ranging from the violet to the orange-red edge of the electromagnetic spectrum (l $ 420 to 610 nm). Under broad band illumination (UV-NIR), the PbS QDs enhance CO 2 photoreduction rates with TiO 2 by a factor of $5 in comparison to unsensitized photocatalysts. X-ray photoelectron spectroscopy (XPS) is used to investigate the deactivation mechanism of the QD sensitizers after prolonged photoexcitation. The synthesis, characterization, and catalytic testing of these PbS sensitized TiO 2 heterostructures will aid the development of more robust, visible light active photocatalysts for carbon management applications.