TY - JOUR
T1 - Cs-doped H4SiW12O40 catalysts for biodiesel applications
AU - Pesaresi, L.
AU - Brown, D. R.
AU - Lee, A. F.
AU - Montero, J. M.
AU - Williams, H.
AU - Wilson, K.
N1 - Funding Information:
This work was supported by the Engineering and Physical Sciences Research Council [EP/E013090/1, EP/F063423]. JMM thanks BP Biofuels and EPSRC for the award of a studentship. AFL thanks the EPSRC for the award of a Leadership Fellowship [EP/G007594/1].
Copyright:
Copyright 2009 Elsevier B.V., All rights reserved.
PY - 2009/5/31
Y1 - 2009/5/31
N2 - 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, N2 gas adsorption, XRD, XPS and NH3 flow calorimetry. Cs substitution promotes recrystallisation of the parent H4SiW12O40 polyoxometallate to the Cs4 salt, 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-xSiW12O40 are strong acids, with ΔHθads(NH3) ranging from -142 to 116 kJ mol-1 with increasing Cs content, consistently weaker than their phosphotungstic analogues. CsxH4-xSiW12O40 materials are active catalysts for both C4 and C8 triglyceride 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.
AB - 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, N2 gas adsorption, XRD, XPS and NH3 flow calorimetry. Cs substitution promotes recrystallisation of the parent H4SiW12O40 polyoxometallate to the Cs4 salt, 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-xSiW12O40 are strong acids, with ΔHθads(NH3) ranging from -142 to 116 kJ mol-1 with increasing Cs content, consistently weaker than their phosphotungstic analogues. CsxH4-xSiW12O40 materials are active catalysts for both C4 and C8 triglyceride 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.
KW - Biodiesel
KW - Green Chemsitry
KW - Heterogeneous catalysis
KW - Heteropolyacid
KW - Solid acid
UR - http://www.scopus.com/inward/record.url?scp=64649102856&partnerID=8YFLogxK
U2 - 10.1016/j.apcata.2009.03.003
DO - 10.1016/j.apcata.2009.03.003
M3 - Article
AN - SCOPUS:64649102856
VL - 360
SP - 50
EP - 58
JO - Applied Catalysis A: General
JF - Applied Catalysis A: General
SN - 0926-860X
IS - 1
ER -