Cs-doped H4SiW12O40 catalysts for biodiesel applications
Cs-doped H4SiW12O40 catalysts for biodiesel applications
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DOI：
10.1016/j.apcata.2009.03.003
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发表时间：
2009-05
影响因子：
5.5
通讯作者：
Lucilla Pesaresi;David R. Brown;A. Lee;J. Montero;H. Williams;K. Wilson
中科院分区：
文献类型：
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作者：
Lucilla Pesaresi;David R. Brown;A. Lee;J. Montero;H. Williams;K. Wilson
合成了通式为CsxH 4 − xSiW 12 O 40（x=0.8-4）的Cs交换硅钨酸催化剂，并通过元素分析、N2气体吸附、XRD、XPS和NH3流动量热法等技术对其进行了表征。Cs取代促进母体H4 SiW 12 O 40多金属氧酸盐重结晶为Cs4盐，通过在Cs0.8-2.8之间的组合物形成稳定的中间相。这种再结晶是伴随着一个显着的上升和随后的孔隙率下降，与最大的中孔体积的材料含有2.8 Cs原子每Keggin单位。量热法显示所有CsxH 4 − xSiW 12 O 40都是强酸，随着Cs含量的增加，ΔHθads（NH3）的范围从−142到116 kJmol − 1，始终弱于它们的磷钨酸类似物。CsxH 4 − xSiW 12 O 40材料是C4和C8甘油三酯酯交换反应以及棕榈酸与甲醇酯化反应的活性催化剂。对于负载≤0.8 Cs/Keggin，（酯交换）活性来自均匀的贡献。然而，更高的取代度导致完全多相催化，其速率与中孔内存在的可接近的酸位点的密度成比例。
Cs exchanged silicotungstic acid catalysts of general formula CsxH4−xSiW12O40(x=0.8–4) have been synthesised and characterised by a range of techniques including elemental analysis, N2gas adsorption, XRD, XPS and NH3flow calorimetry. Cs substitution promotes recrystallisation of the parent H4SiW12O40polyoxometallate to the Cs4salt, via a stable intermediate phase formed at compositions between Cs0.8–2.8. This recrystallisation is accompanied by a pronounced rise and subsequent fall in porosity, with a maximum mesopore volume obtained for materials containing 2.8 Cs atoms per Keggin unit. Calorimetry reveals all CsxH4−xSiW12O40are strong acids, with ΔHθads(NH3) ranging from −142 to 116kJmol−1with increasing Cs content, consistently weaker than their phosphotungstic analogues. CsxH4−xSiW12O40materials are active catalysts for both C4and C8triglyceride transesterification, and palmitic acid esterification with methanol. For loadings ≤0.8 Cs per Keggin, (trans)esterification activity arises from homogeneous contributions. However, higher degrees of substitution result in entirely heterogeneous catalysis, with rates proportional to the density of accessible acid sites present within mesopores.