Enhanced aromatic selectivity by the sheet-like ZSM-5 in syngas conversion

Aromatics are important basic chemicals. However, direct conversion of syngas via the conventional Fischer-Tropsch synthesis produces little aromatics. We presented herein that a bifunctional composite of ZSM-5 in combination with Zn Cr Oxcatalyzes syngas conversion to aromatics. Particularly, ZSM-5 crystals with a sheet-like morphology can enhance significantly the aromatization activity. The lower length ratio of the b/a axes of the crystals, the more aromatics form but without influencing the selectivity of small molecules such as CH4 and C2–C4. Since the acid properties and the Al chemical environment were not altered while the morphology changed, the enhanced aromatic selectivity is likely attributed to the favored diffusion of aromatics in these sheet-like crystals.

Selective conversion of syngas to propane over ZnCrO_x-SSZ-39 OX-ZEO catalysts

Oxide-Zeolite(OX-ZEO) bifunctional catalyst design concept has been exemplified in several processes to direct conversion syngas to value-added chemicals and fuels such as mixed light olefins, ethylene, aromatics and gasoline.Herein we demonstrate that the product can be steered toward liquefied petroleum gas(LPG) with a selectivity up to 89% in hydrocarbons especially propane selectivity reaching 80% at CO conversion of 63% using ZnCrOx-H-SSZ-39 catalyst.Interestingly, the quantity of the acid sites of SSZ-39 does not influence obviously the hydrocarbon distribution but the strength is crucial for selective formation of propane.This finding provides an alternative route of LPG synthesis from a variety of carbon resources via syngas.

Effect of pH on the catalytic performance of PtSn/B-ZrO2 in propane dehydrogenation

Boron-modified ZrO2(B-ZrO2)was synthesized under various pH values(9,10,and 11)and used as the supports of PtSn catalysts(PtSn/B-ZrO2-x)for non-oxidative dehydrogenation of propane.The NH3-TPD and pyridine IR show that only Lewis acid is present and the acid strength increases with the synthesis pH.PtSn/B-ZrO2-10 exhibits the best catalytic performance with an initial propane conversion of 36%and a deactivation rate constant(kd)of 0.0127 h^-1.The XPS results indicate that the electronic properties of Pt and SnOx are affected not only by their interaction but also by the interaction with support.After a careful analysis of the oxygen storage capacity and activity in CO oxidation,it is hypothesized that the interaction between Pt and Sn becomes stronger following the order:PtSn/B-ZrO2-9<PtSn/B-ZrO2-11<PtSn/B-ZrO2-10.The characterization with TPO and Raman on spent catalysts exhibits that more hydrogen deficient coke forms on the support and less coke deposits on the metal surface of PtSn/B-ZrO2-10.The results reveal that the interaction between Pt and Sn is influenced by their respective interaction with the support and a moderate interaction between the metal species and the support is desired.

SAPO-34 facilitates the formation of benzene,toluene and xylenes in direct syngas conversion over MnCrO_(x)-SAPO-34-ZSM-5

Direct conversion of syngas to aromatics over metal oxide and zeolite(OXZEO) composite catalysts is promising.However,the selectivity of more valuable products such as benzene,toluene and xylenes(BTX) is limited due to undesired secondary methylation of BTX.Herein,we report that the introduction of SAPO-34 into MnCrO_(x)-ZSM-5 catalyst enhances significantly the formation of BTX without sacrificing the aromatics selectivity.Under optimized conditions,the fraction of BTX in aromatics reaches 64.7% versus 28.9% over the catalyst without SAPO-34.A number of model reaction tests and characterizations reveal that SAPO-34 consumes partially the intermediates such as ketene,by converting them to light olefins.Thus,the methylation of BTX by ketene to heavy aromatics is inhibited over the external acid sites of ZSM-5,leading to an enhanced BTX selectivity in the products.This hybrid catalyst provides an efficient method for highly selective synthesis of BTX from syngas.

A versatile method for the encapsulation of various non-precious metal nanoparticles inside single-walled carbon nanotubes

We present a facile and versatile method for introducing various non-precious metal nanoparticles （NPs） in small nanotubes, such as single-walled carbon nanotubes （SWNTs）, including 3d-metals （V, Mn, Fe and Co）, 4d-metals （Mo）, and 5d-metals （W）. This is realized by oxidizing encapsulated cycloalkene metal carbonyl complexes below their sublimation temperatures. This novel technique is significant because it avoids the diffusion and deposition of metal species on the outer walls of nanotubes, which has been challenging to achieve using the conventional filling methods. High-resolution transmission electron microscopy （HRTEM）, high angle annular dark field scanning transmission electron microscopy （HAADF-STEM）, energy-dispersive X-ray spectroscopy （EDX）, Raman, and X-ray photoelectron spectroscopy （XPS） analyses revealed high filling efficiencies （〉 95% SWNTs filled with metal NPs）. This method also provides a unique approach to fabricate highly dispersed and uniform SWNT-metal nanoparficle encapsulates with lower valence states, which are often not stable in the bulk.