The newly-assisted catalytic mechanism of surface hydroxyl species performed as the promoter in syngas-to-C2 species on the Cu-based bimetallic catalysts

In the conversion process of syngas-to-C_(2)species,the OH species are inevitably produced accompanying the production of key intermediates CH_(x)(x=1-3),traditionally,the function of surface OH species is generally accepted as the hydrogenating reactive species.This work for the first time proposed and confirmed the assisted catalytic mechanism of surface OH species that performed as the promoter for syngas-to-C_(2)species on Cu-based catalysts.DFT and microkinetic modeling results reveal that the produced OH species accompanying the intermediates CH_(x)production on the MCu(M=Co,Fe,Rh)catalysts can stably exist to form OH/MCu catalysts,on which the presence of surface OH species as the promoter not only presented better activity and selectivity toward CH_(x)(x=1-3)compared to MCu catalysts,but also significantly suppressed CH_(3)OH production,providing enough CH_(x)sources to favor the production of C_(2)hydrocarbons and oxygenates.Correspondingly,the electronic properties analysis revealed the essential relationship between the electronic feature of OH/MCu catalysts and catalytic performance,attributing to the unique electronic micro-environment of the catalysts under the interaction of surface OH species.This new mechanism is called as OH-assisted catalytic mechanism,which may be applied in the reaction systems related to the generation of OH species.

Synthesis and characterization of the flower-like La_(x)Ce_(1-x)O_(1.5+δ) catalyst for low-temperature oxidative coupling of methane

Lanthanum-based oxides are promising candidates for low-temperature oxidative coupling of methane(OCM).To further lower the OCM reaction temperature,the Ce doped flower-like La_(2)O_(2)CO_(3)microsphere catalysts were synthesized,achieving a significantly low reaction temperature (375℃) while maintaining high C_(2) hydrocarbon selectivity (43.0%).Doping Ce into the lattice of La_(2)O_(2)CO_(3)created more surface oxygen vacancies and bulk lattice defects,which was in favor of the transformation and migration of oxygen species at 350–400℃.The designed H_(2) temperature-programmed reduction (H_(2)-TPR) experiments provided strong evidence that the low reaction temperature of La_(x)Ce_(1-x)O_(1.5+δ)can be attributed to the transformation and migration of oxygen species,which dynamically generated surface oxygen vacancies for continuous oxygen activation to selectively convert methane.Moreover,designed temperatureprogrammed surface reaction (TPSR) clarified that two kinds of surface oxygen species in La_(x)Ce_(1-x)O_(1.5+δ)catalysts were concerned with catalytic performance,that is,the surface chemisorbed oxygen species for the activation of CH_(2)and the formation of CH_(2)·intermediates,surface La-Ce-O lattice oxygen species that caused the excessive oxidation of CH_(2)·intermediates.Finally,the factors affecting the transformation and migration of oxygen species were explored.

XPS study of potassium-promoted molybdenum carbides for mixed alcohols synthesis via CO hydrogenation

The X-ray photoelectron spectroscopy （XPS） was used to investigate the surface characteristic of potassium-promoted or un-promoted both β-Mo2C and α-MoC1-x pretreated by syngas at different temperatures,and the promotional effect of potassium on the catalytic performance was also studied.XPS results revealed that the content of surface Mo and its valence distribution between β-Mo2C and α-MoC1-x were quite different.Promoted by potassium,the remarkable changes were observed for surface composition and valence of Mo distribution over β-Mo2C.Potassium had strong electronic effect on β-Mo2C,which led to a higher Mo4＋ content.On the contrary,potassium had little electronic effect on α-MoC1-x,and K-Mo interaction was weak.Therefore,Mo0 and Mo2＋ became the dominant species on the catalyst surface,and the Mo4＋ content showed almost no increase as the pretreatment temperature enhanced.In terms of catalytic performance of molybdenum carbides,the increase in Mo0 most likely explained the increase in hydrocarbon selectivity,yet Mo4＋ might be responsible for the alcohols synthesis.

Nickel and potassium co-modified β-Mo_2C catalyst for CO conversion

Nickel and potassium co-modified β-Mo2C catalysts were prepared and used for CO hydrogenation reaction. The major products over β-Mo2C were C1-C4 hydrocarbons, only few alcohols were obtained. Addition of potassium resulted in remarkable selectivity shift from hydrocarbons to alcohols at the expense of CO conversion over β-Mo2C. Moreover, it was found that potassium enhanced the ability of chain propagation with a higher C2＋OH production. Modified by nickel,β-Mo2C showed a relatively high CO conversion, however, the products were similar to those of pure β-Mo2C. When co-modified by nickel and potassium,β-Mo2C exhibited high activity and selectivity towards mixed alcohols synthesis, and also the whole chain propagation to produce alcohols especially for the stage of C1 OH to C2OH was remarkably enhanced. It was concluded that the Ni and K had, to some extent, synergistic effect on CO conversion.

Catalytic performance of Fe modified K/Mo_2C catalyst for CO hydrogenation

Fe modified and un-modified K/Mo2C were prepared and investigated as catalysts for CO hydrogenation reaction. Compared with K/Mo2C catalyst, the addition of Fe increased the production of alcohols, especially the C2＋OH. Meanwhile, considerable amounts of C5＋ hydrocar- bons and C2= -C4= were formed, whereas methane selectivity greatly decreased. Also, the activity and selectivity of the catalyst were readily affected by the reaction pressure and temperature employed. According to the XPS results, Mo4＋ might be responsible for the production of alcohols, whereas the low valence state of Mo species such as Mo^0 and/or Mo^2＋ might be account for the high activity and selectivity toward hydrocarbons.

Multi-objective optimization of frequency and damping of vertical stabilizer skin structure placed with variable-angle tows

The vibration characteristics of composite vertical stabilizer skin structures play a critical role in damping effects designed for overcoming the air disturbances experienced by aircraft structural components during flight.The first-order fundamental frequencies and their corresponding damping characteristics of the vertical stabilizer skin structure tow-steered by automatic fiber placement technique were optimized with the parameterized trajectories and plies as design variables.Firstly,the vibration and damping numerical models were derived based on Kirchhoff laminate theory,the Rayleigh-Ritz method,and the Strain Energy Method.Then the optimization model was developed by adopting the self-adaptive Differential Evolution Multi-objective optimization algorithm and incorporating the solution method of Pareto Front.The constraints of this optimization model considered the experimentally obtained minimum turning radius of prepregs tow-steered in automatic fiber placement process obtained from experimental tests.Finally,the comparison of numerical simulation results was conducted for the optimized trajectories and the conventional straight trajectories under various boundary conditions,and the numerical results were partially validated through damping and frequency tests.The results indicate the vibration characteristics of the composite vertical stabilizer skin structure can be enhanced to a large extent by optimizing fiber trajectories,and the enhancement percentage is affected by the boundary conditions of the actual structure.

Fischer-Tropsch Synthesis over Alumina- Supported Cobalt-Based Catalysts: Effect of Support Variables

Different kinds of aluminum precursors were obtained from precipitating ammonium bicarbonate, ammonium carbonate, and saturated ammonium bicarbonate, then, boehmite (AlO(OH)), ammonium alumina carbonate hydroxide (AACH) and their mixture were obtained, and then, different kinds of alumina were obtained after calcination. Three catalysts supported on the different alumina were obtained via impregnating cobalt and ruthenium by incipient wetness. The effects of different precipitants on composition of precursors were?studied by XRD, FTIR, and TGA. The property and structure of alumina were studied by XRD and BET. The supported catalysts were studied by characterizations of XRD and H2-TPR, and the catalytic performance for Fischer-Tropsch synthesis (FTS) were evaluated at a fix-bed reactor. The relations among the composition of precursors, the property of alumina and the catalytic performance of supported catalysts were researched thoroughly.

Plant–rodent interactions after a heavy snowfall decrease plant regeneration and soil carbon emission in an old-growth forest

Background:Climate extremes are likely to become more common in the future and are expected to change ecosystem processes and functions.As important consumers of seeds in forests,rodents are likely to affect forest regeneration following an extreme weather event.In April 2015,we began a field experiment after an extreme snowfall event in January 2015 in a primary forest that was>300 years old.The heavy snow broke many tree limbs,which presumably reduced the numbers of seeds produced.Two treatments(rodent exclusion and rodent access)were established in the forest,in which rodent exclusion were achieved by placing stainlessness nets around the plot borders.Plant abundance,plant species richness,soil properties,soil microbial community composition,basal and substrate-induced respiration were determined in December 2017.Results:Plant abundance and species richness significantly increased,but soil microbial biomass decreased with rodent exclusion.Urease activity and soil basal respiration also significantly decreased with rodent exclusion.Most other soil properties,however,were unaffected by rodent exclusion.The relative effects of multiple predictors of basal respiration were mainly explained by the composition of the soil microbial community.Conclusions:After a heavy snowfall in an old-growth forest,exclusion of rodents increased plant regeneration and reduced microbial biomass and soil basal respiration.The main factor associated with the reduction in soil basal respiration was the change in the composition of the soil microbial community.These findings suggest that after a heavy snowfall,rodents may interfere with forest regeneration by directly reducing plant diversity and abundance but may enhance carbon retention by indirectly altering the soil microbial community.

Rubber-based agroforestry systems modify the soil fungal composition and function in Southwest China

Rubber-based agroforestry systems have been recognized as a practical and sustainable solution to promote the development of agriculture and the environment.However,interactions between fungal communities and these systems are still not sufficiently investigated.In this study,we compared the abundance,diversity,and community composition of soil fungi in four treatments,including rubber monoculture and three rubber-based agroforestry treatments involving intercropping with Camellia sinensis,Coffea liberica,and Theobroma cacao.The results revealed that the community composition exhibited significant variation between the four different treatments,while the overall soilα-diversity was relatively stable across all treatments.Soil pH and soil organic carbon were significantly related to the structure of the fungal community.In particular,the complexity of the functional fungal network increased in response to agroforestry treatments,promoting beneficial fungi and suppressing certain plant pathogens.These results suggest that rubber-based agroforestry systems can promote the health of soil microbial community composition,and therefore provide an effective approach to enhancing soil quality.

Effects of plant growth regulators on the rapid proliferation of shoots and root induction in the Chinese traditional medicinal plant Atractylodes macrocephala

We developed an efficient plant regeneration protocol for rapidly propagating Atractylodes macrocephala Koidz,an important traditional Chinese medicinal plant,via shoot organogenesis.Shoot multiplication was induced on Murashige-Skoog(MS)medium supplemented with various concentrations of N-phenyl-N-1,2,3-thidiazol-5-ylurea(TDZ),6-benzylaminopurine(BA)andα-naphthaleneacetic acid(NAA).Rooting was induced on half-strength MS medium supplemented with NAA and indolebutyric acid(IBA).The maximum mean number of shoots(5.61)was obtained from a single explant by the combined effect of 1.08μmol/L NAA and 2.25μmol/L TDZ.The longest roots and a minimum number of roots were produced when they were cultured in a medium without plant growth regulators.The shortest roots and the largest number of roots were observed in the medium supplemented with 2.7μmol/L NAA.

Effects of soil organism interactions and temperature on carbon use efficiency in three different forest soils

Microbial carbon use efficiency(CUE)affects the soil C cycle to a great extent,but how soil organisms and the abiotic environment combine to influence CUE at a regional scale remains poorly understood.In the current study,microcosms were used to investigate how microbial respiration,biomass,and CUE responded to biotic and abiotic factors in natural tropical,subtropical,and temperate forests.Soil samples from the forests were collected,sterilized,and populated with one or a combination of three types of soil organisms(the fungus Botrytis cinerea,the bacterium Escherichia coli,and the nematode Caenorhabditis elegans).The microcosms were then kept at the mean soil temperatures of the corresponding forests.Microbial respiration,biomass,and CUE were measured over one-month incubation period.The results showed that microbial biomass and CUE were significantly higher,but microbial respiration lower in the subtropical and temperate forest soils than in tropical forest soil.Biotic factors mainly affected CUE by their effect on microbial biomass,while temperature affected CUE by altering respiration.Our results indicate that temperature regulates the interactive effects of soil organisms on microbial biomass,respiration,and CUE,which would provide a basis for understanding the soil C cycle in forest ecosystems.

Global Identification of Significantly Expressed Genes in Developing Endosperm of Rice by Expression Sequence Tags and cDNA Array Approaches

Rice endosperm plays a very important role in seedling germination and determines the qualities of rice grain. Although studies on specific gene categories in endosperm have been carried out, global view of gene expression at a transcription level In rice endosperm Is still limited. To gain a better understanding of the global and tissue-specific gene expression profiles In rice endosperm, a cDNA library from rice endosperm of immature seeds was sequenced. A cDNA array was constructed based on the tentative unique transcripts derived from expression sequence tag （EST） assembling results and then hybridized with cDNAs from five different tissues or organs including endosperm, embryo, leaf, stem and root of rice. Significant redundancy was found for genes encoding prolamin, glutelin, allergen, and starch synthesis proteins, accounting for ~34% of the total ESTs obtained. The cDNA array revealed 87 significantly expressed genes In endosperm compared with the other four organs or tissues. These genes included 13 prolamin family proteins, 17 glutelin family proteins, 12 binding proteins, nine catalytic proteins and four ribosomal proteins, indicating a complicated biological processing in rice endosperm. In addition, Northern verification of 1,4-alpha-glucan branching enzyme detected two isoforms in rice endosperm, the larger one of which only existed in endosperm.