Citrate-mediated sol–gel synthesis of Al-substituted sulfated zirconia catalysts for α-pinene isomerization

Abdallah I.M. Rabee, Lee Durndell, Nasr Fouad, Lucia Frattini, Mark Isaacs, Adam Lee, Gamal A.H. Mekhemer, Vannia Cristina dos Santos, Karen Wilson, Mohamed I. Zaki

Research output: Contribution to journalArticlepeer-review

Abstract

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 increase 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.
Original languageEnglish
Pages (from-to)206-212
JournalMolecular Catalysis
Volume458
Issue numberPart B
Early online date11 Nov 2017
DOIs
Publication statusPublished - 1 Oct 2018

Bibliographical note

Funding: Alexander von Humboldt foundation (Bonn) , EPSRC (EP/K000616/2 and EP/G007594/4). Royal Society Industry Fellowship, government of Egypt.

Keywords

  • Citrate mediated sol-gel
  • Sulfated zirconia
  • Terpenes
  • α-pinene
  • Solid acidity

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