Polar-discontinuity-retaining a-site intermixing and vacancies at srtio3/laalo3 interfaces

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Polar-discontinuity-retaining A-site intermixing and vacancies at SrTiO3/LaAlO3SrTiO_{3}/LaAlO_{3} interfaces

Our anomalous surface x-ray diffraction study of the interface between SrTiO3(001) substrates and thin polarfilms of LaAlO3shows La/Sr interdiffusion leading to neutrally charged Sr1−1.5xLaxO layers. From a thickness oftwo unit cells, the LaAlO3film’s interior retains its polar stacking sequence, which is compensated by a cationiccompositional change of the substrate’s terminating TiO2layer. While such valence-retainingA-site intermixingdoes not resolve the polar catastrophe, it may be a general feature at oxide interfaces influencing the electronicand magnetic properties

Higher alcohols through CO hydrogenation over CoCu catalysts: Influence of precursor activation

Bimetallic CoCu model catalysts were investigated for the synthesis of higher alcohols using catalytic CO hydrogenation according to the Fischer-Tropsch technology. Emphasis was placed on revealing the influence of the activation conditions. Accordingly, catalyst precursors were activated in argon, hydrogen, syngas (CO/H2), and CO under atmospheric conditions and at elevated temperatures (370 °C). All catalyst precursors were prepared via oxalate coprecipitation in the absence of a classic support. Alcohol selectivities between 30 and ∼40% (up to ∼50% for the sum of alcohols and alkenes) were obtained with an Anderson-Schulz-Flory (ASF) chain lengthening probability maximizing the slate up to C6. Detailed catalysis and characterization studies were performed using a Co2Cu1 catalyst composition. The catalytic performances of the H2- and syngas-activated Co2Cu1 catalyst were similar. While the CO-activated catalyst shows significantly higher catalytic activity and ASF chain lengthening probability, the alcohol selectivities are lower than those of H2- or syngas-activated ones. All catalysts required time on stream for several hours to achieve steady-state catalytic performance. Co 2Cu1 catalysts were characterized by temperature- programmed decomposition (TPDec), in situ N2 physisorption (Brunauer-Emmett-Teller), transmission electron microscopy (TEM), and in situ X-ray photoelectron spectroscopy (XPS). The data indicate major restructuring occurs during activation. An "onion-like" graphitic carbon shell was observed via TEM for the CO-activated Co2Cu1 catalyst, which probably originated mainly from the Boudouard reaction (2CO + [ ] ad → Cad + CO2). This interpretation is in accordance with the TPDec profiles and XPS results. The latter also indicates that syngas and CO activation lead to higher than nominal Co/Cu surface ratios. The surface segregation of Co in the presence of CO atmospheres is interpreted on the basis of Co@Cu core-shell structured particles. © 2014 American Chemical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe