以中孔洞二氧化矽為載體之金屬觸媒的製備及在硼烷氨水解產氫之應用

Preparation of Mesoporous Silica-Supported Metal Catalysts and the Application in Hydrogen Generation from Ammonia Borane

俞品如(Pin-Ju Yu)

指導教授 ： 陳玉惠

中原大學/理學院/化學研究所/博士(2017年)

https://doi.org/10.6840/cycu201700046

摘要

本研究首先藉由二種中孔洞二氧化矽，有序的MCM-41及無序的二氧化矽氣凝膠(SAG)，分別由界面活性劑製備MCM-41及離子熔液當模板利用溶膠-凝膠法製備SAG。利用簡單快速的微波法在90秒內製備Pt/MCM-41及Pt/SAG 觸媒。結果顯示，MCM-41、SAG皆具有高的比表面積，Pt成功還原至MCM-41 (Pt/MCM-41)、SAG (Pt/SAG) ，皆可達18 wt % 還原率。在各種環境之下催化硼烷氨水溶液水解產氫結果顯示，Pt/SAG催化活性優於Pt/MCM-41。進行五次重複利用產氫反應後， Pt/SAG觸媒仍保有初始的催化活性。
其次，藉由一個簡單的化學還原方法，合成Co/SAG的奈米複合材料，在水解硼烷氨水溶液當作催化劑。結果顯示，Co/SAG產氫速度比以相同方式合成出來的 Co/MCM-41觸媒高出41%。這結果是因為Co奈米粒子在SAG (小於5 nm) 比MCM-41中較小且有較好的分散性，可由TEM可以觀察到。Co/SAG相較於大部分以Co當金屬的觸媒具有較好的轉換頻率(3013 ml H2 min-1 gCo-1)和低活化能( 46.4 kJ mol-1)。
最後，將Co和Pt前驅物透過前述簡易的化學還原法和方便操作且有效率的微波法，製備一系列的Pt-Co雙金屬觸媒還原在SAG，命名為PCx/SAG， x = 1–6。將所有製備出來的Pt-Co雙金屬觸媒，在溫度303K以及金屬莫耳數與硼烷氨莫耳數比為0.05 (M/AB = 0.05)的條件下，催化0.33 wt% 硼烷氨水溶液水解反應。結果顯示，PC3/SAG觸媒，(Pt : Co = 0.27 : 0.73 (莫耳比))，在水解硼烷氨表現出最高的催化效能。與Pt/SAG和 Co/SAG 混合物做比較，使用PC3/SAG為觸媒完全產生氫氣反應的時間減少大約5.6倍。PC3/SAG 具有協同催化效應，導致具有高轉換頻率 (123.1 mol H2 min-1 molmetal-1) 和低活化能 (30.2 kJ mol-1)。除此之外，經過重複利用PC3/SAG觸媒5次，水解硼烷氨水溶液後 H2/NH3BH3莫耳比仍然保持3.0的理論值，而且完成水解反應所需的時間皆少於3分鐘。本研究結果顯示PC3/SAG雙金屬觸媒在水解硼烷氨水溶液系統上具有很高的催化效率。

關鍵字

中孔洞二氧化矽 ； 硼烷氨 ； 觸媒 ； 產氫

並列摘要

In this study, first, two mesoporous silica supports, an ordered MCM-41 and an amorphous silica aerogel (SAG), were prepared with a surfactant and an ionic liquid by the sol-gel process as the template, respectively. The Pt/MCM-41 and Pt/SAG catalysts, were then synthesized by the simple, efficient microwave-assisted method from MCM-41 and SAG, respectively within 90 seconds. The results indicated that both MCM-41 and SAG had high surface area, and the Pt/SAG and Pt/SAG catalysts with approximately 18 wt % loading of Pt were successfully synthesized. It is found that Pt/SAG exhibited higher catalytic activity in hydrogen generation from aqueous NH3BH3 (AB) solution than Pt/MCM-41 under all the conditions studied. After 5 recycles, its initial catalytic ability was retained for the used Pt/SAG.
Then, a Co/SAG nanocomposite synthesized by a facile chemical reduction was used as an alternative catalyst for hydrogen generation from aqueous AB. The result showed that Co/SAG exhibited 41% higher hydrogen generation rate for the AB hydrolysis than the Co/MCM-41 prepared by the same reduction method. This is attributed to the fact that the Co nanoparticles were smaller (less than 5 nm in diameter) and better deposited in SAG than MCM-41 as observed in the TEM micrographs. It is also found that the Co/SAG catalyst delivered superior turnover frequency (3013 ml H2 min-1 gmetal-1) and activation energy (46.4 kJ mol-1) than most of the Co-based catalysts reported.
Finally, a series of platinum–cobalt bimetallic catalysts supported on SAG, referred to as PCx/SAG, x = 1–6, were prepared by the facile chemical reduction and the simple, efficient microwave-assisted method mensioned above using Co and Pt precursors. All of the Pt–Co bimetallic catalysts were applied for the generation of hydrogen from an aqueous solution containing 0.33 wt% AB at a metal to AB molar ratio (M/AB) of 0.05 at 303 K. The PC3/SAG, with molar ratio of Pt : Co = 0.27 : 0.73, exhibited the highest catalytic efficiency for the hydrolysis of AB. As compared with that observed for the corresponding mixture of Pt/SAG and Co/SAG, the time required to complete hydrogen generation using the PC3/SAG catalyst was reduced by approximately 5.6 times. A synergistic catalytic effect was observed from PC3/SAG, leading to a high turnover frequency (123.1 mol H2 per min per mol metal) and a low activation energy (30.2 kJ mol-1). Furthermore, after reusing the catalyst for 5 cycles, the H2/NH3BH3 molar ratio by the dehydrogenation of aqueous AB by PC3/SAG retained an ideal value of 3.0, and complete hydrolysis was achieved each time in less than 3 min. The results of this study indicate that the bimetallic catalyst PC3/SAG prepared herein is highly efficient for the generation of hydrogen from an aqueous AB solution.

並列關鍵字

Mesoporous Silica ； Ammonia Borane ； Catalyst ； Hydrogen Generation

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