Revealing Size Dependent Structural Transitions in Supported Gold Nanoparticles in Hydrogen at Atmospheric Pressure.

The enhancement of the catalytic activity of gold nanoparticles with their decreasing size is often attributed to the increasing proportion of low-coordinated surface sites. This correlation is based on the paradigmatic picture of working gold nanoparticles as perfect crystal forms having complete and static outer surface layers whatever their size. This picture is incomplete as catalysts can dynamically change their structure according to the reaction conditions and as such changes can be eventually size-dependent. In this work, using aberration-corrected environmental electron microscopy, size-dependent crystal structure and morphological evolution in gold nanoparticles exposed to hydrogen at atmospheric pressure, with loss of the face-centered cubic crystal structure of gold for particle size below 4 nm, are revealed for the first time. Theoretical calculations highlight the role of mobile gold atoms in the observed symmetry changes and particle reshaping in the critical size regime. An unprecedented stable surface molecular structure of hydrogenated gold decorating a highly distorted core is identified. By combining atomic scale in situ observations and modeling of nanoparticle structure under relevant reaction conditions, this work provides a fundamental understanding of the size-dependent reactivity of gold nanoparticles with a precise picture of their surface at working conditions.

Novel high-pressure/high-temperature reactor cell for in situ and operando x-ray absorption spectroscopy studies of heterogeneous catalysts at synchrotron facilities.

This paper presents the development of a novel high-pressure/high-temperature reactor cell dedicated to the characterization of catalysts using synchrotron x-ray absorption spectroscopy under operando conditions. The design of the vitreous carbon reactor allows its use as a plug-flow reactor, monitoring catalyst samples in a powder form with a continuous gas flow at high-temperature (up to 1000 °C) and under high pressure (up to 1000 bar) conditions, depending on the gas environment. The high-pressure/high-temperature reactor cell incorporates an automated gas distribution system and offers the capability to operate in both transmission and fluorescence detection modes. The operando x-ray absorption spectroscopy results obtained on a bimetallic InCo catalyst during CO2 hydrogenation reaction at 300 °C and 50 bar are presented, replicating the conditions of a conventional microreactor. The complete setup is available for users and permanently installed on the Collaborating Research Groups French Absorption spectroscopy beamline in Material and Environmental (CRG-FAME) sciences and French Absorption spectroscopy beamline in Material and Environmental sciences at ultra-high dilution (FAME-UHD) beamlines (BM30 and BM16) at the European Synchrotron Radiation Facility in Grenoble, France.

Valuation of Costs in Health Economics During Financial and Economic Crises: A Case Study from Lebanon.

In 2019, we embarked on a study on the economic burden of multiple sclerosis (MS) in Lebanon, in collaboration with a premier Lebanese MS center. This coincided with a triple disaster in Lebanon, comprising the drastic economic and financial crisis, the COVID-19 pandemic, and the consequences of the explosion of Beirut's port. Specifically, the economic and financial turmoil made the valuation of costs challenging. Researchers could face similar challenges, particularly in low- and middle-income countries (LMICs) where economic crises and recessions are recurrent phenomena. This paper aims to discuss steps taken to overcome the fluctuation of the prices of resources to get a valid valuation of societal costs during times of a financial and economic crisis. In the absence of local costing data and guidelines for conducting cost-of-illness (COI) studies, this paper provides empirical recommendations on the valuation of costs that are particularly relevant in LMICs. We recommend (1) clear reporting and justification of the country-specific context, year of costing, assumptions, data sources, and valuation methods, as well as the indicators used to adjust cost for inflation during different periods of fluctuation of prices; (2) collecting prices of each resource from multiple and various sources; (3) conducting a sensitivity analysis; and (4) reporting costs in local currency and Purchasing Power Parity dollars (PPP$). Precision and transparency in reporting prices of resources and their sources are markers of the reliability of the COI studies.

Supported Molybdenum Carbide and Nitride Catalysts for Carbon Dioxide Hydrogenation.

Catalysts based on molybdenum carbide or nitride nanoparticles (2-5 nm) supported on titania were prepared by wet impregnation followed by a thermal treatment under alkane (methane or ethane)/hydrogen or nitrogen/hydrogen mixture, respectively. The samples were characterized by elemental analysis, volumetric adsorption of nitrogen, X-ray diffraction, and aberration-corrected transmission electron microscopy. They were evaluated for the hydrogenation of CO2 in the 2-3 MPa and 200-300°C ranges using a gas-phase flow fixed bed reactor. CO, methane, methanol, and ethane (in fraction-decreasing order) were formed on carbides, whereas CO, methanol, and methane were formed on nitrides. The carbide and nitride phase stoichiometries were tuned by varying the preparation conditions, leading to C/Mo and N/Mo atomic ratios of 0.2-1.8 and 0.5-0.7, respectively. The carbide activity increased for lower carburizing alkane concentration and temperature, i.e., lower C/Mo ratio. Enhanced carbide performances were obtained with pure anatase titania support as compared to P25 (anatase/rutile) titania or zirconia, with a methanol selectivity up to 11% at 250°C. The nitride catalysts appeared less active but reached a methanol selectivity of 16% at 250°C.