Zn-Promoted H‑ZSM‑5 for Endothermic Reforming of <i>n</i>‑Hexane at High Pressures

The addition of Zn to H-ZSM-5 zeolites was studied for application to endothermic reforming in hypersonic aircraft engines. Temperature-programmed-desorption (TPD)/thermogravimetric-analysis (TGA) measurements with 2-propanamine on two H­(Zn)-ZSM-5 samples showed that at low ion-exchange levels, less than 0.5 Zn/Al, each Zn cation displaces one Brønsted-acid site. Although rates for <i>n</i>-hexane conversion at 633 and 823 K and at a pressure of 137 bar decreased with the loss of Brønsted sites, Zn promotion greatly increased the production of H₂ and the formation of small aromatic molecules. FTIR of adsorbed acetonitrile-<i>d</i>₃ and calorimetric measurements of adsorbed CO at 195 K indicate that the exchanged Zn cations form Lewis-acid centers. A model in which the Zn cations, acting as Lewis-acid centers, polarize intermediates formed at Brønsted sites is presented as a way of understanding the observations

Proportion of tuberculosis cases by month of report.

<p>Month begins with January and is abbreviated by first letter. It shows that TB cases exhibit a peak in March and a trough in December across the entire study period.</p

The ACF graph and PACF graph of the ARIMA (0,1,0) × (0,1,0)₁₂ model.

<p>ACF=autocorrelation function, PACF=partial autocorrelation fuction. After taking a non-seasonal and seasonal difference, the TB report rate series shows dominant peaks in the autocorrelation functions lags 12, 24 and 36 months indicating a strong seasonal pattern in the report rate of TB in Hubei Province, China.</p

The ACF graph and PACF graph of the residuals for the ARIMA (2,1,0) × (0,1,1)₁₂ model.

<p>ACF=autocorrelation function, PACF=partial autocorrelation fuction. As their correlation values are not outside the confidence intervals (CI) limits, the residuals error is considered to be white noise indicating that this model is appropriate for prediction. </p

The selection of the spread of the GRNN-ARIMA model.

<p>ARIMA=the autoregressive integrated moving average; GRNN=the generalized regression neural network. The spread values between 0.5 and 1.5 with an interval of 0.05 were selected to find the minimum RMSE for the testing samples. When the spread was 0.95, the RMSE was lowest.</p

Two models’ fitting and prediction curves and the actual tuberculosis report rate series.

<p>ARIMA=the autoregressive integrated moving average; GRNN=the generalized regression neural network.</p

Time series of tuberculosis report rate in Hubei Province, China between Jan 2004 and Dec 2011.

<p>Time series of tuberculosis report rate in Hubei Province, China between Jan 2004 and Dec 2011.</p