Selective hydrogenation of acetylene on Pd/SiO2 catalysts promoted with Ti, Nb and Ce oxides

Transition-metal oxides added to Pd/SiO₂ improve significantly the activity and the ethylene selectivity of the catalyst in acetylene hydrogenation, which is caused by the interaction between the oxides and the Pd surface similar to the case of the oxide-supported catalysts. It has been confirmed through experiments that metal oxides spread on and modify both geometrically and electronically the Pd surface after the catalyst is reduced at 500°C. Such a behavior of metal oxides in the catalyst is correlated well with their promotional effect on the catalyst performance. That is, the oxides on the Pd surface retard the sintering of the dispersed Pd particles, suppress the adsorption of ethylene in the multiply-bound mode, and facilitate the desorption of ethylene produced by acetylene hydrogenation. Among the three metal oxides examined in this study, Ti oxide is found to have the most promotional effect.     

Promotional roles of second metals in catalyzing methane decomposition over the Ni-based catalysts for hydrogen production: A critical review

The thermocatalytic decomposition (TCD) of methane is considered as a milestone towards the production of valuable CO_x-free hydrogen and carbon nanomaterials without the use of steam or O₂. Previous reviews have been aimed at methane decomposition over the different catalysts, such as nickel-based catalysts, non-nickel-based catalysts, metal oxide-supported catalysts, and carbon-supported catalysts. The Ni-based catalysts are suitably applied for methane TCD process due to their high activity and low cost. However, the loss of activity and/or stability with reaction time is one of the most notable challenges in the use of Ni-based catalysts, and a number of studies on the roles of various factors in overcoming such a problem can be found in the literature. Recently, the use of the second metal as a promoter to control catalyst deactivation has attracted much attention. The present review focuses on classification of the different promoters based on the periodic table of elements, such as alkali metals, alkaline earth, transition metals, noble metals, and rare earth metals, and makes a detailed discussion on promotional roles in influencing their physicochemical properties and catalytic performance of the Ni-based catalysts. The generalized structure-performance relationship of the metals-doped catalysts may give an appreciated reference to the design of catalysts with highly pure hydrogen production and carbon nanomaterials. In addition, this review also covers the works on effects of the promoters on nature and morphology of the formed carbon nanomaterials. The use of transition metals (Fe, Co or Cu), noble metal (Pd or Pt), and rare earth metal (La) with a suitable loading as a promoter influenced performance and lifespan of the catalyst and the interaction of Ni particles with the support. Among these promoters, Cu, Pd, La, and Cu–Pd as a dopant have demonstrated superior performance, which was attributed to the capability of these elements in prohibiting carbon accumulation on the active Ni components.     

Titanium nitride promoted Ni-based SBA-15 catalyst for dry reforming of methane

Titanium nitride (TiN) promoted nickel catalysts were synthesized and employed as an alternative catalyst in dry reforming of methane (DRM). The series of this catalyst containing various amount of Ni and TiN was prepared in two steps, direct synthesis of SBA-15 in the presence of TiN and the impregnation of Ni. The influence of Ni and TiN loading on DRM reaction was investigated using a feed ratio of CH₄/CO₂ = 1, at 700 °C and atmospheric pressure for a duration of 4 h. The promising catalysts, that gave the highest feed conversions and product yields, were selected for further investigation, compared to non-promoted Ni catalyst using the same conditions but for 12 h of reaction. The results showed that the performance of Ni catalyst was improved by the incorporation of TiN. The modified catalysts provided not only high catalytic activity but also enhancement of coke resistance.     

助剂对沸腾床渣油加氢催化剂结构性能的影响

考察了单一助剂和复合助剂组合对沸腾床渣油加氢催化剂结构性能的影响。结果表明助剂的加入显著改善了催化剂的加氢活性及转化率,可以选择不同的助剂组合来制备适用于沸腾床工艺的渣油加氢催化剂。     

合成气直接制低碳烯烃铁基催化剂的研究进展

评述了近年来有关合成气直接制低碳烯烃铁基催化剂的研究进展,重点分析了铁基催化剂的活性相、载体、助剂对催化剂的活性、选择性等方面的影响,并对未来铁基催化剂的发展方向进行了展望。     

The analysis of core promoter sequences based on their chemical features

The biochemical behaviors of promoter sequences are closely associated with their chemical properties and structures. In this study, an approach to the analysis of promoter sequences was developed based on the chemical features in DNA sequences. Utilizing the chemical parameters of nucleotides, a string of character sequence was translated into numerical sequences, and then the profiles of chemical properties in the sequence can be observed, which are helpful to better understanding for the behaviors of the sequence. The proposed approach was applied to the analysis of core promoter sequences of Escherichia coli K-12. Apart from the validation of the motifs at the − 35 and − 10 regions, several possible functional sites were observed, and the interaction mechanism between promoter sequence and RNA Polymerase holoenzyme was explored. The obtained results indicate that the consensus of important chemical features is higher than that of the characters in sequences, and our study could provide biologists some valuable hints.     

低温磷化液的研究

通过正交实验 ,确定了以亚硝酸盐、镍盐、钼酸盐、有机添加剂等为促进剂的低温磷化液。得到的磷化膜经硫酸铜点滴实验 ,出现红色的时间为 12 0s ,3 %NaCl水溶液浸泡 2h ,试样表面无锈蚀现象 ,其耐蚀性能优良     

The study of the uncalcined Au catalyst and inorganic salts on direct gas-phase epoxidation of propylene

This paper presents the results of the propylene epoxidation in co-presence of hydrogen and oxygen on both dried and calcined Au catalysts, which were prepared by liquid grafting method using Me₂Au(acac) as a precursor and trimethylsilylated Ti-MCM-48 as a support. The calcined catalyst shows PO activity at temperatures much higher and wider than the dried one. Addition of inorganic salts greatly modified the catalytic behaviors. CsNO₃ could be a promising promoter whereas KBr led to the production of propionaldehyde instead of propylene oxide.     

Quantitative measurement of chromium's ability to promote adhesion

Using atomic force spectroscopy, we investigated the adhesion-promoting ability of chromium. An intermediate layer of chromium can overcome the low adhesion between metal films and silicon dioxide. For the first time, we quantitatively studied this experimentally well known fact. We compared the adhesion between chromium and different substrates such as gold, silver, mica, and silicon dioxide and, beyond that, the adhesion between silicon dioxide and the same substrates. To avoid additional effects due to water, we chose ethanol as a nonpolar solvent. Taking the interfacial energies of the surfaces with the liquid into account eliminates the direct influence of the fluid medium on the adhesion of the solid material. The results we obtained corroborate the experimental fact of higher adhesion of chromium with the chosen substrates, as well as substantiate the value of chromium as an adhesion promoter. The adhesion of chromium-coated probes on gold, silicon dioxide, and mica is higher than the adhesion of silicon dioxide probes on the same substrates.