The surface chemistry of carbon materials is predominantly explored using x-ray photoelectron spectroscopy (XPS). However, many published papers have critical failures in the published analysis, ...stemming from an ill-informed approach to analyzing the spectroscopic data. Herein, a discussion on lineshapes and changes in the spectral envelope of predominantly graphitic materials are explored, together with the use of the D-parameter, to ascertain graphitic content, using this information to highlight a simple and logical approach to strengthen confidence in the functionalization derived from the carbon core-level spectra.
The selective oxidation of methane, the primary component of natural gas, remains an important challenge in catalysis. We used colloidal gold-palladium nanoparticles, rather than the same ...nanoparticles supported on titanium oxide, to oxidize methane to methanol with high selectivity (92%) in aqueous solution at mild temperatures. Then, using isotopically labeled oxygen (O₂) as an oxidant in the presence of hydrogen peroxide (H₂O₂), we demonstrated that the resulting methanol incorporated a substantial fraction (70%) of gas-phase O₂. More oxygenated products were formed than the amount of H₂O₂ consumed, suggesting that the controlled breakdown of H₂O₂ activates methane, which subsequently incorporates molecular oxygen through a radical process. If a source of methyl radicals can be established, then the selective oxidation of methane to methanol using molecular oxygen is possible.
The selective oxidation of methane to methanol, using H2O2, under mild reaction conditions was studied using bimetallic 1 wt % AuPd/TiO2 prepared by stabilizer-free sol-immobilization. The ...as-prepared catalysts exhibited low, unselective oxidation activity and deleterious H2O2 decomposition, which was ascribed to the small mean particle size of the supported AuPd nanoparticles. Heat treatments were employed to facilitate particle size growth, yielding an improvement in the catalyst turnover frequency and decreasing the H2O2 decomposition rate. The effect of support phase was studied by preparing a range of AuPd catalysts supported on rutile TiO2. The low surface area rutile TiO2 yielded catalysts with effective oxygenate production but poor H2O2 utilization. The influence of the rutile-TiO2 support was investigated further by producing catalysts with a lower metal loading to maintain a consistent metal loading per square meter compared to the 1 wt % AuPd/P25 TiO2 catalyst. When calcined at 800 °C, the 0.13 wt % AuPd catalyst demonstrated significantly improved turnover frequency of 103 h–1. In contrast, the turnover frequency was found to be ca. 2 h–1 for the rutile-supported 1 wt % AuPd catalyst calcined at 800 °C. The catalysts were probed by electron microscopy and X-ray photoelectron spectroscopy to understand the influence of particle size and oxidation state on the utilization of H2O2 and oxygenate productivity. This work shows that the key to highly active catalysts involves the prevention of deleterious H2O2 decomposition, and this can be achieved through carefully controlling the nanoparticle size, metal loading, and metal oxidation state.
There remains considerable debate over the active form of gold under operating conditions of a recently validated gold catalyst for acetylene hydrochlorination. We have performed an in situ x-ray ...absorption fine structure study of gold/carbon (Au/C) catalysts under acetylene hydrochlorination reaction conditions and show that highly active catalysts comprise single-site cationic Au entities whose activity correlates with the ratio of Au(I):Au(III) present. We demonstrate that these Au/C catalysts are supported analogs of single-site homogeneous Au catalysts and propose a mechanism, supported by computational modeling, based on a redox couple of Au(I)-Au(III) species.
Primarily due to its inherent redox chemistry, ceria (CeO
2
) is of use in many diverse areas of research. However, there is a wealth of misinterpretation of the oxygen spectra when discussing the ...result of damage or reduction to the CeO
2
lattice, especially with regard to a signal in this region attributed to oxygen vacancies. In this paper, it is shown that this peak cannot be due to vacancies and that a better understanding of the changes in stoichiometry of CeO
2
is best viewed from that of the Ce(III) component when considered in tandem with the O 1s signal.
Au/C catalysts prepared using aqua regia as a solvent display superior activity in the hydrochlorination reaction of acetylene to vinyl chloride monomer. A synergistic effect between HCl and HNO3 is ...observed, which is linked to the nucleation of Au nanoparticles. Display omitted
► Impregnated Au/C catalyst with aqua regia as a solvent displayed superior activity in the hydrochlorination reaction of acetylene to vinyl chloride monomer. ► A synergistic effect between HCl and HNO3 is present, driving the Au nanoparticles nucleation process over the carbon support. ► The impregnating acid mixture can affect the carbon support enriching the presence of oxygen functional groups. ► The reaction occurs over Au3+ centres at the Au/C interface.
Au/C catalysts are effective materials for the gas phase hydrochlorination of acetylene to vinyl chloride monomer, and to date, the most effective catalyst preparation protocol makes use of impregnation using aqua regia. In the present study, the effect of this solvent is evaluated and discussed in detail by modifying the ratio of HCl and HNO3 and the temperature of the impregnation step. These factors are observed to affect the Au3+/Au0 ratio of the final catalyst, in addition to the modification of the functional groups of the carbon used as support. The results can be rationalised by the oxidation effect of HNO3 on both the gold nanoparticles and the functional groups on the carbon surface, as well as a nucleation effect of HCl towards gold over the carbon support.
A mixed oxide support containing Ce, Zr, and Al was synthesized using a physical grinding method and applied in the oxidative dehydrogenation of propane using CO2 as the oxidant. The activity of the ...support was compared with that of fully formulated catalysts containing palladium. The Pd/CeZrAlO x material exhibited long-term stability and selectivity to propene (during continuous operation for 140 h), which is not normally associated with dehydrogenation catalysts. From temperature-programmed desorption of NH3 and CO2 it was found that the catalyst possessed both acidic and basic sites. In addition, temperature-programmed reduction showed that palladium promoted both the reduction and reoxidation of the support. When the role of CO2 was investigated in the absence of gas-phase oxidant, using a temporal analysis of products (TAP) reactor, it was found that CO2 dissociates over the reduced catalyst, leading to formation of CO and selective oxygen species. It is proposed that CO2 has the dual role of regenerating selective oxygen species and shifting the equilibrium for alkane dehydrogenation by consuming H2 through the reverse water-gas-shift reaction. These two mechanistic functions have previously been considered to be mutually exclusive.
The mechanism by which pharmacologic administration of the hormone FGF21 increases energy expenditure to cause weight loss in obese animals is unknown. Here we report that FGF21 acts centrally to ...exert its effects on energy expenditure and body weight in obese mice. Using tissue-specific knockout mice, we show that βKlotho, the obligate coreceptor for FGF21, is required in the nervous system for these effects. FGF21 stimulates sympathetic nerve activity to brown adipose tissue through a mechanism that depends on the neuropeptide corticotropin-releasing factor. Our findings provide an unexpected mechanistic explanation for the strong pharmacologic effects of FGF21 on energy expenditure and weight loss in obese animals.
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•FGF21 acts directly on the nervous system to stimulate sympathetic nerve activity•The effects of FGF21 on sympathetic outflow require corticotropin-releasing factor•The central actions of FGF21 are required for it to cause weight loss
FGF21 promotes weight loss and improves insulin sensitivity when administered to obese rodents, monkeys, and humans. Owen et al. find in obese mice that these therapeutic effects require FGF21 to act directly on the brain, where it stimulates sympathetic nerve activity via the neuropeptide CRF to activate brown fat.
Rapid advances in artificial intelligence (AI) and automation technologies have the potential to significantly disrupt labor markets.While AI and automation can augment the productivity of some ...workers, they can replace the work done by others and will likely transform almost all occupations at least to some degree. Rising automation is happening in a period of growing economic inequality, raising fears of mass technological unemployment and a renewed call for policy efforts to address the consequences of technological change. In this paper we discuss the barriers that inhibit scientists frommeasuring the effects of AI and automation on the future of work. These barriers include the lack of high-quality data about the nature of work (e.g., the dynamic requirements of occupations), lack of empirically informed models of key microlevel processes (e.g., skill substitution and human–machine complementarity), and insufficient understanding of how cognitive technologies interact with broader economic dynamics and institutional mechanisms (e.g., urban migration and international trade policy). Overcoming these barriers requires improvements in the longitudinal and spatial resolution of data, as well as refinements to data on workplace skills. These improvements will enable multidisciplinary research to quantitatively monitor and predict the complex evolution of work in tandem with technological progress. Finally, given the fundamental uncertainty in predicting technological change, we recommend developing a decision framework that focuses on resilience to unexpected scenarios in addition to general equilibrium behavior.
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