The pre-reduction of the industrially relevant Cr-VI/SiO2 Phillips catalyst by cyclohexene at room temperature was investigated by means of operando XANES, Diffuse Reflectance UV-Vis and transmission FT-IR spectroscopies. It was found that cyclohexene efficiently reduces the surface chromates sites (Cr-VI) at room temperature to give mainly divalent chromium sites and aldehyde by-products, which are rapidly converted in ester species. These by-products remain in strong interaction with the reduced chromium sites, defining a complex and tunable ligand sphere, which controls the entrance of incoming molecules, including ethylene. Unlike the Cr-VI/SiO2 catalyst, the cyclohexene-reduced Cr/SiO2 catalyst polymerizes ethylene already at room temperature with no induction time. The reactivity of cyclohexene with the Cr-VI species mimics that of ethylene during the induction period on Cr-VI/SiO2 catalyst, simplified by the absence of the further polymerization step. Hence, the results discussed in this work are potentially useful to understand what happens during the induction period in the presence of ethylene

Pre-reduction of the Phillips CrVI/SiO2 catalyst by cyclohexene: A model for the induction period of ethylene polymerization

BARZAN, CATERINA;DAMIN, Alessandro Ali;BUDNYK, Andriy;ZECCHINA, Adriano;BORDIGA, Silvia;GROPPO, Elena Clara
2016-01-01

Abstract

The pre-reduction of the industrially relevant Cr-VI/SiO2 Phillips catalyst by cyclohexene at room temperature was investigated by means of operando XANES, Diffuse Reflectance UV-Vis and transmission FT-IR spectroscopies. It was found that cyclohexene efficiently reduces the surface chromates sites (Cr-VI) at room temperature to give mainly divalent chromium sites and aldehyde by-products, which are rapidly converted in ester species. These by-products remain in strong interaction with the reduced chromium sites, defining a complex and tunable ligand sphere, which controls the entrance of incoming molecules, including ethylene. Unlike the Cr-VI/SiO2 catalyst, the cyclohexene-reduced Cr/SiO2 catalyst polymerizes ethylene already at room temperature with no induction time. The reactivity of cyclohexene with the Cr-VI species mimics that of ethylene during the induction period on Cr-VI/SiO2 catalyst, simplified by the absence of the further polymerization step. Hence, the results discussed in this work are potentially useful to understand what happens during the induction period in the presence of ethylene
2016
337
45
51
http://www.elsevier.com/inca/publications/store/6/2/2/8/5/8/index.htt
Chromium; Ethylene polymerization; Heterogeneous catalysis; Induction period; Phillips catalyst; Catalysis; Physical and Theoretical Chemistry SUPPORTED CHROMIUM CATALYSTS; DIFFUSE-REFLECTANCE SPECTROSCOPY; NEAR-EDGE STRUCTURE; IN-SITU; XANES SPECTROSCOPY; TRANSITION-METALS; SURFACE-COMPOUNDS; CR/SIO2 CATALYST; OXIDE CATALYSTS; K-EDGE
Barzan, Caterina; Damin, Alessandro A.; Budnyk, Andriy; Zecchina, Adriano; Bordiga, Silvia; Groppo, Elena
File in questo prodotto:
File Dimensione Formato  
Barzan_JCatal_2016_CrVI-CyHex.pdf

Accesso riservato

Descrizione: Pdf editoriale
Tipo di file: PDF EDITORIALE
Dimensione 720.29 kB
Formato Adobe PDF
720.29 kB Adobe PDF   Visualizza/Apri   Richiedi una copia
Barzan_2016_OPENACCESS.pdf

Accesso aperto

Descrizione: Post Print
Tipo di file: POSTPRINT (VERSIONE FINALE DELL’AUTORE)
Dimensione 972.14 kB
Formato Adobe PDF
972.14 kB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/1570329
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 23
  • ???jsp.display-item.citation.isi??? 20
social impact