以中孔徑矽分子篩(SBA15)摻雜金屬觸媒在氫氣與二氧化碳中還原多氯聯苯之探討

Hydrodechlorination of Polychlorinated Biphenyls with Pt＋Pd/ SBA15 in Hydrogen Gas and Carbon Dioxide

陳怡君(Yi-Chun Chen)

指導教授 ： 葉華光

中原大學/理學院/化學研究所/碩士(2010年)

https://doi.org/10.6840/cycu201000059

摘要

多氯聯苯（polychlorinated biphenyls，簡稱PCBs）是一種相當穩定又好用的絕緣體，在以前多被用在電容器、變壓器、可塑劑、潤滑油等。初期，人們不知道多氯聯苯具毒性，將多氯聯苯廢料丟棄在環境中。多氯聯苯不易被生物代謝或自然界分解，在環境中會經由食物鏈的傳遞而生物聚集於各種生物體內，對生物造成危害，人們若食用遭污染的生物，最終對人類造成危害。

超臨界流體特色為兼具氣態和液態的特性，如高擴散性及低黏性。本研究選用超臨界二氧化碳作為溶劑，其優點為不可燃、低活性、無毒性，臨界溫度、臨界壓力，（31.1℃、72.8 atm）易達成，且超臨界二氧化碳為公認綠色化學溶劑。

本研究的目的是尋找一個有效且節能的方法來還原多氯聯苯，使其降解成低毒性或無毒性的物質。本研究使用鉑和鈀金屬摻雜中孔洞矽分子篩（SBA-15）來製備混合金觸媒（Pt＋Pd/SBA-15），探討其對多氯聯苯氫化脫氯的可行性。

本研究利用初濕含浸法製備混合金屬觸媒，後經高溫鍛燒，配製 4 % Pt-1 % Pd/ SBA15與1 % Pt-4 % Pd/ SBA15。再將觸媒加上氫氣進行對多氯聯苯的氫化脫氯反應，比較兩種觸媒的還原能力，實驗樣品用GC-MS和GC-ECD檢測。實驗結果顯示在30℃、50℃、100℃的溫度下，反應時間30分鐘，4 % Pt-1 % Pd/ SBA15都能完全將多氯聯苯家族還原成聯二環已烷，質量平衡也都介於90%到104%之間。

在另一個不同實驗設計中，以1 % Pt-4 % Pd/ SBA15在室溫下，對BZ#3 (4-monochlorobiphenyl)進行30、60、90、120分鐘反應時間之實驗，在較短反應時間條件下(30到90分鐘)，得到聯苯、苯基環己烷、聯二環已烷三種產物。但經過120分鐘的反應後，只剩下聯二環已烷一種產物。本實驗結果顯示以Pt＋Pd/ SBA-15觸媒所進行之氫化脫氯反應是一個逐步的過程，通過形成穩定的中間產物即聯苯和苯基環己烷，而形成最終產物聯二環已烷。

關鍵字

中孔洞矽分子篩 ； 超臨界二氧化碳 ； 多氯聯苯

並列摘要

Developing recyclable and efficient metal catalysts, particularly nanoparticle catalysts, for chemical reactions is an active research area then and now. The goal of this research is to investigate preparation of palladium and platinum metals deposited in the pores of mesoporous materials such as Santa Barbara 15 (SBA-15) by an incipient wetness impregnation (IWI) method and to study catalytic properties of this Pd+Pt/SBA-15 template by investigating the recyclability of the template and the hydrodechlorination efficiency of some polychlorinated biphenyl (PCB) congeners and mixtures in the presence of hydrogen gas.
Hydrodechlorination of a PCB congener, BZ#3 (4-monochlorobiphenyl), on a 4% Pt-1% Pd/SBA15 template was performed at 30℃、50 ℃ and 100 ℃. The results showed that even at 30 ℃, BZ#3 can be completely reduced to bicyclohexyl, suggesting that this mixed metal catalyst very effectively lowers the activation energy of the reduction reaction, a phenomenon which has yet been reported so far. Hydrodechlorination of other homologs in the PCB family showed similar results, all reaching 100% with reduction efficiency with mass balance equal or better than 90%.
The catalytic reaction pathway of this mixed metal catalyst was studied by performing experiments for various durations using BZ#3. After shorter reaction times (30 to 90 minutes), biphenyl, cyclohexylbenzene, and bicyclohexyl were all present as the products, whereas after 120 minutes of reduction, only bicyclohexyl is present. This observation suggests that the hydrogenation pathway is a stepwise process, which proceeds by forming stable intermediate products such as biphenyl and cyclohexylbenzene.

並列關鍵字

Santa Barbara 15 ； Polychlorinated Biphenyls ； Supercritical Fluid

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