Citrate-mediated sol–gel synthesis of Al-substituted sulfated zirconia catalysts for α-pinene isomerization
[Display omitted] •A new route to sulfated ZrO2, and Al-substituted ZrO2 (SO4/AlxZrO2) reported.•Citric acid-mediated sol-gel synthesis generates Al3+ substituted t-ZrO2.•Low Al concentrations enhance α-pinene isomerization activity by up to 50%.•Acid strength & selectivity to mono and poly cycl...
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Published in | Molecular catalysis Vol. 458; pp. 206 - 212 |
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Main Authors | , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier B.V
01.10.2018
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Subjects | |
Online Access | Get full text |
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Summary: | [Display omitted]
•A new route to sulfated ZrO2, and Al-substituted ZrO2 (SO4/AlxZrO2) reported.•Citric acid-mediated sol-gel synthesis generates Al3+ substituted t-ZrO2.•Low Al concentrations enhance α-pinene isomerization activity by up to 50%.•Acid strength & selectivity to mono and poly cyclic isomers tuned with Al content.
Solid acids are desirable heterogeneous catalysts for green chemistry, with zirconia and its sulfated analogues offering tunable Lewis/Brønsted character. A new route to sulfated ZrO2, and Al-substituted ZrO2 (SO4/AlxZrO2), via carbonization and calcination of metal citrate gels and their subsequent sulfation by (NH4)2SO4 is reported. Structural and acidic properties of these materials were characterized by XRD, Raman, XPS, TGA-MS, N2 porosimetry, and propylamine and pyridine titration. Parent and sulfated materials all adopted the tetragonal zirconia phase, with Al-substitution (evidenced by contraction of the zirconia lattice parameter) at between 0.38–3.50wt% increasing the surface area but decreasing acid strength, accompanied by an overall increase in total acid site loading and Lewis character. Low Al concentrations enhance α-pinene isomerization activity by up to 50% due to the increased acid site loading, however the Turnover Frequency (TOF) remained constant indicating a common active site. The TOF decreased for Al concentrations >3.5wt% due to a further fall in acid strength, manifest as higher selectivity to polycyclic versus monocyclic products. |
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ISSN: | 2468-8231 2468-8231 |
DOI: | 10.1016/j.mcat.2017.10.029 |