Operando XAS Study of Pt-Doped CeO2 for the Nonoxidative Conversion of Methane

The methane to olefins, aromatics, and hydrogen (MTOAH) process via Pt/CeO$_2$ catalysts poses an attractive route to improve yield and stability for the direct catalytic conversion of methane. In this study, two sets of samples, one composed of PtO$_x$ single sites on ceria and the other with additional Pt agglomerates, were prepared. Both sets of samples showed enhanced catalytic activity for the direct conversion of methane exceeding the performance of pure ceria. Pulsed reaction studies unraveled three reaction stages: reduction of the ceria support during activation, an induction phase with increasing product formation, and finally, stable running of the catalytic reactions. The reduction of ceria was confirmed by X-ray absorption spectroscopy (XAS) after conducting the MTOAH reaction. Operando X-ray absorption spectroscopy at challenging reaction temperatures of up to 975 °C in combination with theoretical simulations further evidenced an increased Pt–Ce interaction upon reaction with CH$_4$. Analysis of the extended X-ray absorption fine structure (EXAFS) spectra proved decoration and encapsulation of the Pt particles by the CeO$_2$/Ce$_2$O$_3$ support or a partial Ce–Pt alloy formation due to the strong metal–support interaction that developed under reaction conditions. Moreover, methyl radicals were detected as reaction intermediates indicating a reaction pathway through the gas-phase coupling of methyl radicals. The results indicate that apart from single-atom Pt sites reported in the literature, the observed Pt–Ce interface may have eased the activation of CH$_4$ by forming methyl radicals and suppressed coke formation, significantly improving the catalytic performance of the ceria-based catalysts in general

Corporate Social Responsibility at African mines: Linking the past to the present

This paper traces the origins of the 'brand' of Corporate Social Responsibility (CSR)employed at large-scale mines across sub-Saharan Africa. Conceived within fortified resource enclaves, the policies adopted and actions taken in the area of CSR at many of the region's large-scale mines today have had had minimal effect on community wellbeing. Further examination reveals that contemporary CSR strategy in the region's mining sector is often a 'repackaging' and 'rebranding' of moves made by major operators during the colonial period and early years of country independence to pacify and engage local communities. Today, this work is being championed as CSR but failing to deliver much change, its impact minimized by the economic and political forces at work in an era of globalization, during which extractive industry enclaves that are disconnected from local economies have been able to flourish. As case study of Ghana, long one of the largest gold mining economies in sub-Saharan Africa, is used to illustrate these points. © 201

Operando XAS Study of Pt-Doped CeO2CeO_2 for the Nonoxidative Conversion of Methane

The methane to olefins, aromatics, and hydrogen (MTOAH) process via Pt/CeO$_2$ catalysts poses an attractive route to improve yield and stability for the direct catalytic conversion of methane. In this study, two sets of samples, one composed of PtO$_x$ single sites on ceria and the other with additional Pt agglomerates, were prepared. Both sets of samples showed enhanced catalytic activity for the direct conversion of methane exceeding the performance of pure ceria. Pulsed reaction studies unraveled three reaction stages: reduction of the ceria support during activation, an induction phase with increasing product formation, and finally, stable running of the catalytic reactions. The reduction of ceria was confirmed by X-ray absorption spectroscopy (XAS) after conducting the MTOAH reaction. Operando X-ray absorption spectroscopy at challenging reaction temperatures of up to 975 °C in combination with theoretical simulations further evidenced an increased Pt–Ce interaction upon reaction with CH$_4$. Analysis of the extended X-ray absorption fine structure (EXAFS) spectra proved decoration and encapsulation of the Pt particles by the CeO$_2$/Ce$_2$O$_3$ support or a partial Ce–Pt alloy formation due to the strong metal–support interaction that developed under reaction conditions. Moreover, methyl radicals were detected as reaction intermediates indicating a reaction pathway through the gas-phase coupling of methyl radicals. The results indicate that apart from single-atom Pt sites reported in the literature, the observed Pt–Ce interface may have eased the activation of CH$_4$ by forming methyl radicals and suppressed coke formation, significantly improving the catalytic performance of the ceria-based catalysts in general

Association of four medication classes and non-suicidal self-injury in adolescents with affective disorders – a retrospective chart review

Background Non-suicidal self-injury (NSSI) behaviour is frequently observed in children and adolescents with psychiatric conditions. Affected individuals are regularly treated with psychotropic drugs, although the impact of these agents on NSSI behaviour remains elusive. Methods We performed a retrospective chart review from clinical routine data in a large cohort (N=1140) of adolescent inpatients with primary affective and non-affective psychiatric disorders according to ICD-10 (mean age=15.3±1.3 years; 72.6% female). Four separate mixed regression models compared the frequency of NSSI between treatment periods without any medication and four medication categories (benzodiazepines, selective serotonin reuptake inhibitors (SSRIs), high- and low-potency antipsychotics). Results In those individuals with affective disorders as the primary diagnosis, periods without medication were associated with significantly lower NSSI/day compared to all four other medication conditions (benzodiazepines p<10−8, antidepressants/SSRIs p=0.0004, high-potency antipsychotics p=0.0009, low-potency antipsychotics p<10 −4). In individuals with a primary diagnosis other than an affective disorder, NSSI was significantly lower during the period without medication compared to the treatment periods with benzodiazepines (p=0.005) and antidepressants/SSRIs (p=0.01). However, NSSI rates in the no-medication condition were comparable to NSSI rates under high-potency (p=0.89) and low-potency antipsychotics (p=0.53). Conclusions The occurrence of NSSI correlates with the treatment with a psychotropic drug in children and adolescents with psychiatric disorders. Due to the retrospective design, it remains elusive to what extent psychotropic drugs might alter the frequency of NSSI in adolescents or if NSSI might indicate a transdiagnostic feature of more pronounced disease severity

Versatile and high temperature spectroscopic cell for operando fluorescence and transmission x-ray absorption spectroscopic studies of heterogeneous catalysts

A modular high-temperature cell consisting of a plug-flow microreactor with a fixed catalyst bed and long heating zone has been established for operando x-ray absorption/fluorescence spectroscopic and diffraction studies. The functionality of the cell is demonstrated for two important areas: emission control using 2 wt. % Pd/Al$_2$O$_3$ acting as a three-way catalyst and direct conversion of methane to olefins and aromatics on a 0.5% Fe/SiO$_2$ catalyst. The performance has been determined by online infrared spectroscopy and mass spectrometry, respectively. In addition, the cell can be combined with optical spectroscopy, such as Raman spectroscopy. The catalyst, present as powdered/sieved samples, can be measured under reaction conditions at temperatures of up to 1050 °C. Another key aspect is a long isothermal heating zone with a small temperature gradient (<3 °C/mm at 1000 °C without reaction) including an inert zone for pre-heating of the reactant gas. Due to the small size of the microreactor and the heating system including a water cooling system, heating/cooling rates of up to 100 °C/min can be achieved. Moreover, due to the compact design and the autonomous control system, the high temperature operando setup fits to the space at the majority of synchrotron beamlines. In many cases, the concentration of the element of interest in the catalysts is low requiring x-ray absorption spectroscopy measurements in the fluorescence measurement mode. Hence, the microreactor was designed to fit such needs as well. More specifically, the case of Fe-containing catalysts was particularly considered by using iron-free materials for the reactor housin

Enhanced Methane Conversion to Olefins and Aromatics by H-Donor Molecules under Nonoxidative Condition

We report that methane conversion to olefins and aromatics over an iron-coated catalytic quartz reactor can be enhanced by hydrogen radicals, which are provided by the thermal decomposition of hydrogen-donor molecules, such as 1,2,3,4-tetrahydronaphthalene (THN) and benzene. For example, methane conversion increases from 19.7% to 25.5% in the presence of 1.41% THN in methane at 1323 K. The onset temperature of C2H4 formation decreases from 1143 to 1073 K by adding 7.7% C6H6 into the methane feed. Isotope experiments further indicate the involvement of H radicals in the reaction, which could activate methane homogeneously according to the reaction: center dot H + CH4 -> H-2 + center dot CH3; this occurs in addition to the heterogeneous activation of methane over iron sites

Methyl radical chemistry in non-oxidative methane activation over metal single sites

Abstract Molybdenum supported on zeolites has been extensively studied as a catalyst for methane dehydroaromatization. Despite significant progress, the actual intermediates and particularly the first C-C bond formation have not yet been elucidated. Herein we report evolution of methyl radicals during non-oxidative methane activation over molybdenum single sites, which leads selectively to value-added chemicals. Operando X-ray absorption spectroscopy and online synchrotron vacuum ultraviolet photoionization mass spectroscopy in combination with electron microscopy and density functional theory calculations reveal the essential role of molybdenum single sites in the generation of methyl radicals and that the formation rate of methyl radicals is linearly correlated with the number of molybdenum single sites. Methyl radicals transform to ethane in the gas phase, which readily dehydrogenates to ethylene in the absence of zeolites. This is essentially similar to the reaction pathway over the previously reported SiO2 lattice-confined single site iron catalyst. However, the availability of a zeolite, either in a physical mixture or as a support, directs the subsequent reaction pathway towards aromatization within the zeolite confined pores, resulting in benzene as the dominant hydrocarbon product. The findings reveal that methyl radical chemistry could be a general feature for metal single site catalysis regardless of the support (either zeolites MCM-22 and ZSM-5 or SiO2) whereas the reaction over aggregated molybdenum carbide nanoparticles likely facilitates carbon deposition through surface C-C coupling. These findings allow furthering the fundamental insights into non-oxidative methane conversion to value-added chemicals

Methyl radical chemistry in non-oxidative methane activation over metal single sites.

Molybdenum supported on zeolites has been extensively studied as a catalyst for methane dehydroaromatization. Despite significant progress, the actual intermediates and particularly the first C-C bond formation have not yet been elucidated. Herein we report evolution of methyl radicals during non-oxidative methane activation over molybdenum single sites, which leads selectively to value-added chemicals. Operando X-ray absorption spectroscopy and online synchrotron vacuum ultraviolet photoionization mass spectroscopy in combination with electron microscopy and density functional theory calculations reveal the essential role of molybdenum single sites in the generation of methyl radicals and that the formation rate of methyl radicals is linearly correlated with the number of molybdenum single sites. Methyl radicals transform to ethane in the gas phase, which readily dehydrogenates to ethylene in the absence of zeolites. This is essentially similar to the reaction pathway over the previously reported SiO2 lattice-confined single site iron catalyst. However, the availability of a zeolite, either in a physical mixture or as a support, directs the subsequent reaction pathway towards aromatization within the zeolite confined pores, resulting in benzene as the dominant hydrocarbon product. The findings reveal that methyl radical chemistry could be a general feature for metal single site catalysis regardless of the support (either zeolites MCM-22 and ZSM-5 or SiO2) whereas the reaction over aggregated molybdenum carbide nanoparticles likely facilitates carbon deposition through surface C-C coupling. These findings allow furthering the fundamental insights into non-oxidative methane conversion to value-added chemicals