Production of propene from 1-butene metathesis reaction on tungsten based heterogeneous catalysts

A new propene production route from 1-butene metathesis has been developed on heterogeneous 10WO3/Al2O3-HY catalysts with different HY contents. It is found that the catalysts play bi-functionally first for the isomerization of 1-butene to 2-butene and then for the cross-metathesis between 1-butene and 2-butene to propene and 2-pentene. The combination of HY zeolite and Al2O3 is prerequisite for the production of propene. The propene yield keeps increasing with the HY content in the range of 10-70 wt%, where 10WO3/Al2O3-70HY exhibits the highest propene yield. The MS-H2-TPR and MS-O2-TPO characterizations indicate that the increase of HY content in the catalysts weakens the interaction between W species and supports, whereas enhance the probability of coking on the metal species and acid sites.

Effect of Reaction Temperature and Pressure on the Metathesis Reaction between Ethene and 2-Butene to Propene on the WO_3/Al_2O_3-HY Catalyst

Effect of reaction temperature and pressure on the metathesis reaction between ethene and 2-butene to propene was studied on the WO3/γ-Al2O3-HY catalyst. The activity is found to increase with elevated temperature and reaches a plateau at 150-240 ℃. After that, the activity undergoes a remarkable decrement at too high temperature. The effect of temperature is elucidated by the oxidation state of tungsten species. The evaluation results also indicate that the stability is dependent on this reaction parameter. Medium pressure （0.5-0.8 MPa） is favorable for stability, while atmospheric pressure or too high pressure （〉1.0 MPa） deteriorates the stability. For explanation, UV Vis, FT-IR, O2-TPO, and TG techniques are used to characterize the spent catalysts.

Construction of monodispersed single-crystalline hierarchical ZSM-5 nanosheets via anisotropic etching

Hierarchical zeolites and single-crystalline zeolite nanosheets(NSs)have been recognized as two separate types of targeting porous materials to overcome the diffusion limitations of traditional bulk zeolites.The synthesis of uniform single-crystalline hierarchical zeolite NSs featured with NS morphology and interconnected mesoporosity,remains rarely reported.In this work,we prepared ZSM-5 zeolites with the above microstructural features via simple alkaline etching.Moreover,both their microstructure and acid strength could be accurately tuned with this approach,resulting in not only higher conversion rate and BTX selectivity but also superior anti-coking performance in the subsequent methanol aromatization reaction.

Robust AUC maximization for classification with pairwise confidence comparisons

Supervised learning often requires a large number of labeled examples,which has become a critical bottleneck in the case that manual annotating the class labels is costly.To mitigate this issue,a new framework called pairwise comparison(Pcomp)classification is proposed to allow training examples only weakly annotated with pairwise comparison,i.e.,which one of two examples is more likely to be positive.The previous study solves Pcomp problems by minimizing the classification error,which may lead to less robust model due to its sensitivity to class distribution.In this paper,we propose a robust learning framework for Pcomp data along with a pairwise surrogate loss called Pcomp-AUC.It provides an unbiased estimator to equivalently maximize AUC without accessing the precise class labels.Theoretically,we prove the consistency with respect to AUC and further provide the estimation error bound for the proposed method.Empirical studies on multiple datasets validate the effectiveness of the proposed method.

Cause analysis of expressway traffic accidents based on accident statistics of Hunan provincial expressway in 2012-2018

Based on the 2012–2018 accident statistics on the Hunan Provincial Expressway in China,this paper analyses the proportion to which various factors contribute to accidents,as well as the trends over time.From 2012 to 2018,the total number of general procedure handling accidents(i.e.major accidents)increased first and then decreased,while the number of accidents and deaths per 1000 kilometres decreased year by year.The total number of simple procedure handling accidents(i.e.minor accidents)increased year by year,but the number of accidents per 1000 kilometres remained relatively stable.Speeding,fatigued driving,improper driving operation,failure to maintain a safe distance from the preceding vehicle and pedestrians entering the expressway are the main causes of general procedure handling accidents.Failure to maintain a safe distance from the preceding vehicle as required and improper driving operation accounted for approximately 2/3 of the simple procedure handling accidents.In view of the accidents caused by these factors,how to use law enforcement,education,science and technology and facilities construction to further reduce the occurrence of expressway traffic accidents is discussed.

Nanosecond and femtosecond lasers based on black arsenic-phosphorus alloys saturable absorber

In this paper, the high-repetition-rate passively Q-switched(PQS) and the femtosecond continuous-wave mode-locked(CWML) lasers are successfully obtained with 2 D black arsenic-phosphorus(b-As P) nanosheets as saturable absorber(SA) at 1 μm for the first time, to the best of our knowledge. The saturable absorption properties and ultrafast carrier dynamics of the 2 D b-As P SA are explored by Z-scan and pump-probe techniques. Moreover, according to the measurement of desired nonlinear optical characteristics of the relaxation time of 27 ps and the modulation depth of 7.14%, the PQS and CWML lasers are demonstrated with the highest repetition rate of 2.26 MHz in the PQS laser and the pulse width of 470 fs in the CWML laser. The results show 2 D b-As P SA has enormous potential for pulse modulation in solid-state bulk lasers.