- 學位論文
雙金屬CoNiB奈米非晶態觸媒之製備與果糖氫化反應
Preparation of Amorphous CoNiB Nano-Catalyst on Hydrogenation of Fructose
摘要
本研究採化學還原法製備不同Co/Ni比例之CoNiB雙金屬觸媒，另引入水溶性PVP高分子穩定劑，製備高分子穩定化觸媒(PVP-CoNiB)。以ICP、BET、TEM、XRD、DSC、XPS瞭解其物理性質，有系統探討CoNiB及PVP-CoNiB觸媒製備變因，藉改變果糖液相氫化反應條件瞭解CoNiB雙金屬觸媒之果糖催化特性並與葡萄糖及轉化糖氫化反應特性做比較。 CoNiB雙金屬觸媒粒徑及粒徑分佈(3.8~5.6 nm)都比NiB(15~50 nm)及CoB(5.5~9.4 nm)觸媒小，添加PVP高分子穩定劑能讓PVP-CoNiB觸媒的粒徑更小更均一(3.1~4.7 nm)。CoNiB雙金屬觸媒整體組成，金屬/硼之元素比值與NiB及CoB單金屬觸媒比值相近，引入高分子PVP並不影響PVP-CoNiB組成中金屬對硼之元素比值。CoNiB與PVP-CoNiB雙金屬觸媒組成分佈均勻，表面Co/Ni比例與整體比例相近。CoNiB、PVP-CoNiB皆為非晶態觸媒，不為CoB與NiB的物理混合物，且具有較佳的熱穩定性。 CoNiB觸媒於果糖及葡萄糖氫化反應最佳Co/Ni比均為6/4，於轉化糖氫化反應最佳Co/Ni比為5/5，活性約為NiB及CoB觸媒的2~3倍。PVP-CoNiB觸媒活性則約為CoNiB觸媒的2倍。CoNiB及PVP-CoNiB觸媒於果糖液相氫化反應中，最佳反應溫度分別為80℃及90℃，大於最佳反應溫度則活性下降，表觀活化能分別為28.4 kJ/mol與27.7 kJ/mol；氫氣壓力之表觀反應級數約為1；果糖濃度之表觀反應級數約為–0.4。CoNiB與PVP-CoNiB觸媒於果糖全程氫化反應甘露糖醇最大產率約為42 ~ 45 %。 CoNiB與PVP-CoNiB觸媒於葡萄糖及轉化糖氫化反應活性遠不及果糖氫化反應，CoNiB與PVP-CoNiB雙金屬觸媒於葡萄糖氫化反應最佳條件與果糖最佳反應條件相同，於轉化糖氫化反應最佳條件則略有差異，最佳反應溫度降為70℃。CoNiB與PVP-CoNiB觸媒於轉化糖全程氫化反應，最大甘露糖醇產率為16 ~ 20 %。
並列摘要
The PVP-stabilized CoNiB catalysts were prepared using the chemical reduction method with NaBH4, dissolving the water-soluble polymer of polyvinylpyrrolidone (PVP) in the precursor salt solution as a protective reagent. The PVP-CoNiB catalysts were characterized and examined for their catalysis on the hydrogenation of fructose and glucose. PVP polymer could adsorb on the nano-particles of CoNiB via a weak coordination bonding and stabilize it; the optimal quantity of PVP (PVP/Ni+Co) in the salt solution for preparing catalysts was around 3~5. The PVP-CoNiB samples were characterized by XRD as an amorphous structure and by TEM with a particle size distribution in the range of 3–5 nm. On catalysis, the PVP-CoNiB catalyst was significantly more active than NiB and CoB for hydrogenating fructose to mannitol. A good yield of mannitol about 42% could be obtained over the PVP-CoNiB catalyst.