CH_4-CO_2 reforming to syngas over Pt-CeO_2-ZrO_2/MgO catalysts: Modification of support using ion exchange resin method

Pt-CeO2-ZrO2/MgO （Pt-CZ/MgO） catalysts with 0.8 wt% Pt, 3.0 wt% CeO2 and 3.0 wt% ZrO2 were prepared by wet impregnation method. Support MgO was obtained using ion exchange resin method or using commercial MgO. XRD, BET, SEM, TEM, DTA-TG and CO2-TPD were used to characterize the catalysts. CH4-CO2 reforming to synthesis gas （syngas） was performed to test the catalytic behavior of the catalysts. The catalyst Pt-CZ/MgO-IE（D） prepared using ion exchange resin exhibits more regular structure, smaller and more unique particle sizes, and stronger basicity than the catalyst Pt-CZ/MgO prepared from commercial MgO. At 1073 K and atmospheric pressure, Pt-CZ/MgO-IE（D） catalyst has a higher activity and greater stability than Pt-CZ/MgO catalyst for CH4-CO2 reforming reaction at high gas hourly space velocity of 36000 mL/（g.h） with a stoichiometric feed of CH4 and C02. Activity measurement and characterization results demonstrate that modification of the support using ion exchange resin method can promote the surface structural property and stability, therefore enhancing the activity and stability for CH4-CO2 reforming reaction.

Complete Oxidation of Methane over Palladium Supported on Alumina Modified with Calcium,Lanthanum,and Cerium Ions

The activity and thermal stability of Pd/Al2O3 and Pd/（Al2O3＋MOx） （M=Ca, La, Ce） palladium catalysts in the reaction of complete oxidation of methane are presented in this study. The catalyst supports were prepared by sol-gel method and they were dried either conventionally or with supercritical carbon dioxide. Then they were impregnated with palladium nitrate solution. The catalysts with unmodified alumina had a high surface area. The activity and thermal stability of the aluminasupported catalyst was also very high. The introduction of calcium, lanthanum, or cerium oxide into alumina support caused a decrease of the surface area in the way dependent on the support precursor drying method. These modifiers decreased the activity of palladium catalysts, and they required higher temperatures for the complete oxidation of methane than unmodified Pd/Al2O3. The improvement of the palladium activity by lanthanum and cerium support modifier was observed only at low temperatures of the reaction.

Mechanistic Study on the Dominant Promotion Effect of Al-/Ti-/Zr-modifications over the VOx/SiO2 UHMWPE Catalysts

Recently, we reported the first VOx/SiO2 ethylene polymerization catalyst for making Cl-free UHMWPE, and found the dominant promotion effects of Al-/Ti-/Zr-modifications over this catalyst system(Macromol. Chem. Phys. 2017, 218, 1600443). In this work, density functional theory is applied to investigate the underlying mechanism of this remarkable promotion effect of Al-/Ti-/Zrmodifications on a molecular and atomic level. The cluster model with V(Ⅲ) is found to be the most possible active site due to its lowest overall energy barrier for monomer insertion, though the process of C2H4 coordination and the subsequent formation of transition state are most energy favored for V(Ⅱ) species. By modifying one of or both V―O―Si in the active model with V―O―M(M = Al, Ti, or Zr),the energy barrier for the binding of the upcoming C2H4 gets lower(particularly for Al-and Zr-modified catalysts), and the transition state also becomes more stable. Generally, the insertion process of C2H4 gets easier after support Al-/Ti-/Zr-modifications. This dominant promotion effect is partially ascribed to the more enriched positive charge distribution on or nearby the V center, and the narrower energy gap between the LUMO of model catalysts and the HOMO of C2H4 for these modified catalysts also contributes much. In addition, the decreased steric hindrance around the V center should be taken into account for the modified models as well. Furthermore, the Br?nsted acidity of the catalysts is investigated by introducing a pendent hydroxyl group to the model catalysts, which has a close contact with the V center. Similar promotion effect of support modification by Al, Ti, and Zr could still be observed.

Patterns of Chromatin-Modifications Discriminate Different Genomic Features in Arabidopsis

Dynamic regulation and packaging of genetic information is achieved by the organization of DNA into chromatin. Nucleosomal core histones, which form the basic repeating unit of chromatin, are subject to various post-translational modifications such as acetylation, methylation, phosphorylation, and ubiquitinylation. These modifications have effects on chromatin structure and, along with DNA methylation, regulate gene transcription.The goal of this study was to determine if patterns in modifications were related to different categories of genomic features, and, if so, if the patterns had predictive value. In this study, we used publically available data（ChIP-chip）for different types of histone modifications（methylation and acetylation） and for DNA methylation for Arabidopsis thaliana and then applied a machine learning based approach（a support vector machine） to demonstrate that patterns of these modifications are very different among different kinds of genomic feature categories（protein, RNA,pseudogene, and transposon elements）. These patterns can be used to distinguish the types of genomic features.DNA methylation and H3K4me3 methylation emerged as features with most discriminative power. From our analysis on Arabidopsis, we were able to predict 33 novel genomic features, whose existence was also supported by analysis of RNA-seq experiments. In summary, we present a novel approach which can be used to discriminate/detect different categories of genomic features based upon their patterns of chromatin modification and DNA methylation.