氫氧化鋁催化劑製程及粉體特性對鋁與水產氫的影響

Processing and Characteristics of aluminum hydroxide catalysts and its influences on the hydrogen generation of Aluminum with Water reaction

許仕傑(Shih-Chieh Hsu)

指導教授 ： 王宏文

中原大學/理學院/化學研究所/碩士(2018年)

https://doi.org/10.6840/cycu201800394

摘要

本研究利用不同條件比例之偏鋁酸鈉、乙醇以及水合成氫氧化鋁，並藉由XRD鑑定發現隨著反應過程中減少添加的乙醇量，位於18.277°和20.305°的Gibbsite相氫氧化鋁特徵鋒會隨偏鋁酸鈉溶液濃度提高而逐漸往右邊靠，特徵鋒變得矮又寬，位於40.798°位置上的Bayerite相氫氧化鋁特徵鋒有所增加，為Gibbsite和Bayerite相之混合相，顯示了氫氧化鋁粉末結晶相的改變。其外觀為片狀結構的粉末之顆粒大小會因乙醇量減少逐漸變大，比表面積相對降低，對於催化產氫的能力有變慢的趨勢。
在經過乙醇與水使用量和催化產氫性的比較的考量後，找到了本研究的最適條件Test-11(偏鋁酸鈉(g):乙醇(mL):水(mL)=5:100:50)，其於冰浴下合成時間僅需1小時，能在鋁:氫氧化鋁:水 = 1:1:200的系統中在105分鐘內100 %產氫完畢，利用Arrhenius equation算出自製氫氧化鋁當催化劑時，鋁/水反應活化能會從158 kJ/mole降至54.89 kJ/mole，與歷屆所研究出的氫氧化鋁相比催化性是相當高的，除了能夠大量製程，產率在83%以上之外，也打破之前研究對於Bayerite相氫氧化鋁具有active site催化性較佳的觀念，合成之Gibbsite相氫氧化鋁顆粒減小後，其催化性更高，推測其具有的活躍位置(active site)比Bayerite相氫氧化鋁更多，是研究中一大發現。
為了使Test-11合成之片狀粉末顆粒大小降低，也嘗試在合成使用CTAB、PEG、NaBH4添加劑去降低其顆粒大小，增加與鋁粉的接觸面，使粉末催化性能夠更強，不過由於反應時溶液濃度高，添加劑在此濃度相對較低，對於粉末合成並無顯著影響。
在研究的最後了解粉末之成長，在偏鋁酸鈉溶液加入乙醇的情況下基本上皆為Gibbsite和Bayerite之混合相，不過在溶液太鹼的時候，一方面粉末要花更多時間才能析出，另一方面粉末一但析出會快速成長，形成較厚且大片之片狀結構，此時結晶性相當好，可利用XRD看到強度高的Gibbsite相特徵峰，而無Bayerite相氫氧化鋁形成。隨添加乙醇的量提高，此時粉末越來越容易析出，析出時間較快，最後形成薄片狀結構，此時粉末結晶性依然不錯，但厚度太薄，故XRD可看到Gibbsite相特徵峰較寬且矮，而Bayerite相氫氧化鋁則是結晶性變佳，此時的特徵峰強度較為明顯。

關鍵字

鋁/水產氫 ； 氫氧化鋁 ； 快速產氫

並列摘要

In this study, sodium hydroxide, sodium aluminate, ethanol, and water in different proportions were employed to synthesize aluminum hydroxide. Through XRD analysis, we found that peaks of aluminum hydroxide with gibbsit phase at 18.277° and 20.305° are evident with decreasing amounts of ethanol during their synthesises. The first peak at 18.277o in XRD becomes short and wide as the concentration of NaAlO2 solution increases. In the mean time, the characteristic peak of the bayerite phase located at 40.798° decreases and turns into a mixed phase of the gibbsite and bayerite phases. It shows that the crystal phase of aluminium hydroxide powder is changing.
The particle size of the powder with the appearance of a sheet structure will gradually become larger due to the decrease in the amount of ethanol, and the ability to catalyze the production of hydrogen tends to become slower.
After considering the comparison of ethanol and water consumption and catalytic hydrogen production, the optimal conditions for the study, Test-11 (sodium metaaluminate(g):ethanol(mL):water(mL)=5:100:50), were found in an ice bath. The synthesis time is only 1 hour. In the system of Al: Al(OH)3:H2O=1:1:200, 100% hydrogen production is completed in 105 minutes. The Arrhenius equation is used to calculate the activation energy for these self-made aluminum hydroxide. The activation energy of Al/water reaction will be reduced from 158 kJ/mole to 54.89 kJ/mole. Compared with those aluminum hydroxides studied in previous years, the catalytic performance is better. Besides a large number of processes, the yield is above 83%. Prior to breaking the study, the Bayerite phase aluminum hydroxide has an active site catalytic ideology. After reducing the synthesized Gibbsite phase aluminum hydroxide particles, the catalytic activity is higher. It is presumed that the active site is higher than the Bayerite phase. More aluminum hydroxide is a major discovery in the study.
In order to reduce the particle size of condition Test-11 Aluminium hydroxide powder, it was also attempted to reduce the particle size by synthesizing CTAB, PEG, and NaBH4 additives, to increase the contact surface with the aluminum powder so that the catalytic power of the powder could be stronger, due to the reaction the concentration of the solution is too high, the concentration of additive is too low in this solution, and there is no significant effect on the powder synthesis.
At the end of the study, the growth of the powder was understood to be essentially a mixed phase of Gibbsite and Bayerite in the presence of ethanol in the sodium metaaluminate solution. However, when the solution is too basic, the powder takes more time to precipitate. On the other hand, as soon as the powder precipitates, it will grow rapidly and form a thick and large sheet-like structure. At this time, the crystallinity is quite good. The high-strength Gibbsite phase characteristic peaks can be observed by XRD without the formation of the Bayerite phase aluminum hydroxide. With the increase of the amount of ethanol added, the powder is more and more easily precipitated, the precipitation time is faster, and finally a lamellar structure is formed. At this time, the crystallinity of the powder is still good, but the thickness is too thin, so the characteristic peak of the Gibbsite phase can be seen by XRD. Wide and short, while the Bayerite phase aluminum hydroxide is crystallinity, the characteristic peak intensity at this time is more obvious.

並列關鍵字

Al/water hydrogen generation ； Aluminum hydroxide ； rapid hydrogen generation

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