奈米非晶態物質結合了非晶結構與奈米尺寸的優點，它們含有較多的表面原子及高度配位不飽和鍵；此外奈米非晶態合金粒子因為具有特殊的化學催化性質，而引起廣泛的注意。本研究以化學還原法，改變各種製備條件，製備一系列的Ni-P-B、Ni-B 與Pt-NiB 奈米非晶合金觸媒。觸媒的製備是以0.1M 的醋酸鎳為先驅鹽類，混和次磷酸鈉水溶液（1 M），再將硼氫化鈉水溶液（1 M）緩慢的加入金屬鹽水溶液中，並在溫度為298 K下以磁石攪拌混合，此時即有黑色顆粒狀的鎳觸媒沈澱。其製備變數包含：(1) 觸媒還原溫度：273 K與298 K、(2) 攪拌混合母液速度：500 rpm 與100 rpm、(3) 觸媒製備溶劑：50 vol. %乙醇水溶液、50 vol. %甲醇水溶液與99.9 %甲醇溶液、(4) 製備氣氛：氮氣與空氣、(5) 不同量的白金添加劑。將此一系列所製備而成的Ni-P-B、Ni-B 與Pt-NiB 奈米鎳觸媒，以氮氣吸附儀、X-光繞射儀、穿透式電子顯微鏡、X-光光電子能譜儀等儀器鑑定其物理與表面性質。由物性鑑定結果，可以得知所合成出來的金屬鎳觸媒粒徑大小皆為奈米尺寸且均為長程無序、短程有序的非結晶型態。不同的製備條件，會影響硼、磷與鎳的結合比例，進而引發其表面積、粒子大小與氫化反應活性等觸媒性質的變化。由XPS 結果可知，硼會將一部份電子給鎳，而磷會部分拉鎳的電子，鎳觸媒經過磷或硼的修飾後，穩定性變佳，不像商用倫尼鎳觸媒一樣，一旦暴露到空氣中就會著火，且對於主要產物對氯苯胺有良好的選擇性。在氮氣流下製備的鎳觸媒，可以有效地避免被溶液中的溶氧與空氣中的氧氣氧化，如此一來，經氮氣沖流下所還原出來的金屬觸媒中即含有較多元素態的鎳。在298 K下通氮氣，製備溶劑為50 vol. %乙醇水溶液，且使用攪拌速度500 rpm混合所生成的Ni-P-B 超細合金觸媒是一系列Ni-P-B 觸媒中粒徑最小的(約7-20 nm)；而在相同參數條件下，所還原而得的Ni-B 超細合金觸媒其粒徑為8-15 nm，此Ni-B 觸媒雖然沒有上述Ni-P-B 觸媒的粒徑小，但其粒徑分佈範圍較窄，也就是此Ni-B 觸媒大小較均勻；也就是說在相同製備條件下所合成出來的Ni-B 觸媒，其粒徑分佈會較Ni-P-B 均勻。將對氯硝基苯的選擇性氫化反應作為鎳金屬觸媒的反應活性測試，探討Ni-P-B、Ni-B 與Pt-NiB 奈米非晶合金觸媒間之催化性質的差異。最後結果發現：在298 K下使用劇烈磁石攪拌(500 rpm)通以氮氣，製備溶劑為50 vol. %甲醇水溶液的條件下所製備的Ni-B 觸媒擁有最佳的反應活性而且對於主要產物(對氯苯胺)的選擇率>99 % (此氫化反應條件為：反應溶劑99.9 %甲醇、反應溫度373K，反應氫氣壓力1.2 MPa )。於此種觸媒中再添加3 wt. %的白金，可使對氯硝基苯在反應溫度 333 K下，一小時內轉化完畢且對於對氯苯胺的選擇率>99 %。另外，在氫化反應溶劑部分發現，使用絕對甲醇代替絕對乙醇作為反應溶劑可以大幅提昇對氯硝基苯氫化反應活性。 The nanomaterials, combining the features of amorphous and nanometer powers, have more surface atoms and a higher concentration of coordinately highly unsaturated sites. Nanometer amorphous alloy powders have attracted extensive attention due to their unique isotropic structural and chemical properties. A series of ultrafine Ni-P-B, Ni-B and Pt-NiB amorphous alloy catalysts with various conditions were prepared by the chemical reduction method. The following parameters were studied: (1) reduction temperature (273 K and 298 K), (2) stirring speed (vigorous magnetic stirring 500 rpm and mild agitation 100 rpm), (3) gas atmosphere (nitrogen stream and air), (4) preparation medium and (5) additives. A series of nickel catalysts were prepared by mixing nickel acetate and sodium hypophosphite in preparation medium. The solution of sodium borohydride in excess amount was then added dropwise into the mixture to ensure full reduction of nickel cations. The solutions of nickel salt (0.1 M) and sodium hypophosphite (1 M) were mixed first and the solution of sodium borohydride (1 M) was then added dropwise into the mixture to prepared Ni-P-B materials. Similar method was used to synthesize Ni-B and Pt-NiB samples. These catalysts were characterized by N2 sorption, powder X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The catalysts were tested by liquid phase hydrogenation of p-chloronitrobenzene at 1.2 MPa hydrogen pressure in a batch reactor. The effects of preparation conditions such as temperature, stirring speed and sheltering gas on the particle size, surface compositions, electronic states of surface atoms and catalytic activities of the nickel catalysts were studied. The XRD patterns of these Ni-P-B, Ni-B and Pt-NiB materials reveal an amorphous state. Raney nickel catalyst was included for comparison. The preparation conditions had significant influence on the particle size and surface compositions of the catalyst. All of the catalysts prepared in this study had nanosized particles and were much more active than Raney nickel catalyst. Boron combined with nickel metal in the samples was found to donate electrons to the nickel metal and phosphorus was found to accept electrons from the nickel metal. The catalysts prepared under sheltering gas (N2 flow) could prevent from the oxidation of Ni by the soluble oxygen in water and had metallic state of nickel. The Ni-P-B catalyst prepared at 298 K with vigorous stir had a smaller particle size than that prepared at 273 K. The catalyst prepared with vigorous stir at 298 K under N2 stream yielded the smallest particles and resulted in the highest activity. This activity of Ni-B catalysts is superior to Ni-P-B catalysts in the same preparation conditions and the particle sizes of Ni-B catalysts are more uniform than Ni-P-B catalysts. Sample 3Pt-NiB-MeOH (1/2)-298-500-N2 can fully convert p-chloronitrobenzene to p-chloroaniline within 50 minutes when the reaction temperature was 333 K. Three weight percent of platinum additives is more suitable in the hydrogenation reaction of p-chloronitrobenzene. The reaction condition also has pronounced effect on the catalytic activity. Using methanol as the reaction medium significantly increased the conversion of p-chloronitrobenzene, compared to that using ethanol as the reaction medium. The selectivity of p-chloroaniline was greater than 99% in each of the cases.
