Disentangling the activity-selectivity trade-off in catalytic conversion of syngas to light olefins.

Breaking the trade-off between activity and selectivity has been a long-standing challenge in the field of catalysis. We demonstrate the importance of disentangling the target reaction from the secondary reactions for the case of direct syngas conversion to light olefins by incorporating germanium-substituted AlPO-18 within the framework of the metal oxide-zeolite (OXZEO) catalyst concept. The attenuated strength of the catalytically active Brønsted acid sites allows enhancing the targeted carbon-carbon coupling of ketene intermediates to form olefins by increasing the active site density while inhibiting secondary reactions that consume the olefins. Thus, a light-olefins selectivity of 83% among hydrocarbons and carbon monoxide conversion of 85% were obtained simultaneously, leading to an unprecedented light-olefins yield of 48% versus current reported light-olefins yields of ≤27%.

Tuning the Crystal Phase to Form MnGaOx -Spinel for Highly Efficient Syngas to Light Olefins.

The oxide-zeolite (OXZEO) catalyst design concept has been demonstrated in an increasing number of studies as an alternative avenue for direct syngas conversion to light olefins. We report that face-centered cubic (FCC) MnGaOx -Spinel gives 40 % CO conversion, 81 % light olefins selectivity, and a 0.17 g gcat -1 h-1 space-time yield of light olefins in combination with SAPO-18. In comparison, solid solution MnGaOx (characterized by Mn-doped hexagonal close-packed (HCP) Ga2 O3 ) with a similar chemical composition gives a much inferior activity, i.e., the specific surface activity is one order of magnitude lower than the spinel oxide. Photoluminescence (PL), in situ Fourier-transform infrared (FT-IR), and density functional theory (DFT) calculations indicate that the superior activity of MnGaOx -Spinel can be attributed to its higher reducibility (higher concentration of oxygen vacancies) and the presence of coordinatively unsaturated Ga3+ sites, which facilitates the dissociation of the C-O bond via a more efficient ketene-acetate pathway to light olefins.

Chemistry of Ketene Transformation to Gasoline Catalyzed by H-SAPO-11.

Although ketene has been proposed to be an active intermediate in a number of reactions including OXZEO (metal oxide-zeolite)-catalyzed syngas conversion, dimethyl ether carbonylation, methanol to hydrocarbons, and CO2 hydrogenation, its chemistry and reaction pathway over zeolites are not well understood. Herein, we study the pathway of ketene transformation to gasoline range hydrocarbons over the molecular sieve H-SAPO-11 by kinetic analysis, in situ infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy. It is demonstrated that butene is the reaction intermediate on the paths toward gasoline products. Ketene transforms to butene on the acid sites via either acetyl species following an acetic acid ketonization pathway or acetoacetyl species with keto-enol tautomerism following an acetoacetic acid decarboxylation pathway when in the presence of water. This study reveals experimentally for the first time insights into ketene chemistry in zeolite catalysis.

Achieving the Widest Range of Syngas Proportions at High Current Density over Cadmium Sulfoselenide Nanorods in CO2 Electroreduction.

Electroreduction of CO2 is a sustainable approach to produce syngas with controllable ratios, which are required as specific reactants for the optimization of different industrial processes. However, it is challenging to achieve tunable syngas production with a wide ratio of CO/H2 , while maintaining a high current density. Herein, cadmium sulfoselenide (CdSx Se1-x ) alloyed nanorods are developed, which enable the widest range of syngas proportions ever reported at the current density above 10 mA cm-2 in CO2 electroreduction. Among CdSx Se1-x nanorods, CdS nanorods exhibit the highest Faradaic efficiency (FE) of 81% for CO production with a current density of 27.1 mA cm-2 at -1.2 V vs. reversible hydrogen electrode. With the increase of Se content in CdSx Se1-x nanorods, the FE for H2 production increases. At -1.2 V vs. RHE, the ratios of CO/H2 in products vary from 4:1 to 1:4 on CdSx Se1-x nanorods (x from 1 to 0). Notably, all proportions of syngas are achieved with current density higher than ≈25 mA cm-2 . Mechanistic study reveals that the increased Se content in CdSx Se1-x nanorods strengthens the binding of H atoms, resulting in the increased coverage of H* and thus the enhanced selectivity for H2 production in CO2 electroreduction.

Oxidative Stress Response Induced by Butachlor in Zebrafish Embryo/Larvae: The Protective Effect of Vitamin C.

The widespread contamination and persistence of the herbicide butachlor in the environment resulted in the exposure of non-target organisms. The present study investigated the toxicity effect of butachlor (1-15 µmol/L) and the protective effect of vitamin C (VC) against butachlor-induced toxicity in zebrafish. It was found that butachlor significantly increased the mortality and malformation rates in a dose-dependent manner, which caused elevation in reactive oxygen species (ROS) and malondialdehyde (MDA) after 72 h exposure. Compared with butachlor treatment group, the protective effect of VC against butachlor-induced toxicity were observed after adding 40, 80 mg/L VC respectively. VC significantly decreased the mortality, malformation rates, ROS, MDA, and normalized antioxidant enzymes activities of zebrafish after 72 h exposure. The result shows VC has mitigative effect on butachlor-induced toxicity and it can be used as an effective antioxidant in aquaculture.

Clinical and Economic Impact of Empirical Extended-Infusion Piperacillin-Tazobactam in a Community Medical Center.

BACKGROUND: Current medical center practice allows for the automatic conversion of all piperacillin/tazobactam orders from intermittent to extended infusion (EI). OBJECTIVE: To compare the clinical and cost impact of empirical extended-infusion piperacillin/tazobactam. METHODS: All consecutive patients treated with piperacillin/tazobactam for >48 hours were reviewed for inclusion. Patients were stratified into 2 groups: (1) traditional infusion (TI), preprotocol implementation, and (2) EI, postprotocol implementation. Patient demographics and primary and secondary diagnoses were extracted from the hospital discharge database. All patients were assessed for the primary end point of all cause 14-day in-hospital mortality. Secondary outcomes included length of hospital stay, duration of antibiotic therapy, cost per treatment course, and occurrence of Clostridium difficile infection. RESULTS: A total of 2150 patients were included (EI = 632; TI = 1518). After adjusting for comorbidity, length of stay, and age, 14-day in-hospital mortality was similar between groups (odds ratio = 1.16; 95% CI = 0.85-1.58; P = 0.37). Length of stay was similar between the EI group versus TI (mean ± SD: 12.5 ± 9.58 days vs 11.8 ± 9.58 days, respectively; P = 0.10) after adjusting for age and Chalson-Deyo comorbidity index. Total cost per treatment course was reduced in the EI group by 13% compared with the TI group ($565.90 ± $257.70 vs $648.30 ± $349.20, respectively; P < 0.0001). CONCLUSION: Automatic substitution of EI for TI piperacillin/tazobactam is safe and associated with significant cost savings. EI piperacillin/tazobactam was not associated with a reduction in mortality or length of stay.