Development of a high-performance nanostructured V2O5/SnO2 catalyst for efficient benzene hydroxylationby Peter R. Makgwane, Suprakas S. Ray

Applied Catalysis A: General

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Year
2015
DOI
10.1016/j.apcata.2014.12.024
Subject
Process Chemistry and Technology / Catalysis

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Applied Catalysis A: General 492 (2015) 10–22

Contents lists available at ScienceDirect

Applied Catalysis A: General jou rn al hom epage: www.elsev ier .com/ locate /apcata

Develo ctu catalys

Peter R. M a DST-CSIR Nat h, Pret b Department o a r t i c l

Article history:

Received 17 A

Received in revised form 8 December 2014

Accepted 11 December 2014

Available online 19 December 2014

Keywords:

Vanadium oxide

Tin oxide

Nanostructure

Mixed oxide

Hydroxylation

Benzene

V2O5/ ostru ylation of benzene to phenol using H2O2 as the terminal oxidant. The structure of the catalysts was studied using various techniques, such as XRD, Raman spectroscopy, SEM, EDX, TEM/HRTEM, STEM-HAADF, and

H2-TPR and the adsorption/desorption of nitrogen. The Raman study supported the formation of certain monomeric and polymeric surface vanadium species and a crystalline V2O5 phase on their respective dehydrated mixed V2O5/SnO2 nanostructured catalysts depending on the vanadium loading. TEM stud1. Introdu

The co performanc atom utiliz for sustain central them are also de developme from both t the liquidhydroxylati ∗ Correspon

E-mail add (P.R. Makgwan http://dx.doi.o 0926-860X/© ies revealed the morphology of V2O5 and SnO2 to be characterized by the formation of nanoparticles with a size of approximately 20 nm. Moreover, the dispersion of V2O5 on SnO2 was also found to be influenced by V2O5 loading where a high loading of 20 wt% exhibited an agglomeration of particles, which affected its catalytic activity. The V2O5/SnO2 catalysts resulted in modified redox properties, as evidenced by the

H2-TPR results. These structural developments of mixed V2O5/SnO2 presented a highly active catalyst for the hydroxylation of benzene to phenol affording up to a 34% conversion, while preserving a phenol selectivity of 96% for a sample of V2O5/SnO2 containing 10 wt% V2O5. The catalytic results indicated that the vanadium content in V2O5/SnO2 played an important role not only in improved substrate conversion but also in preserving a high selectivity for phenol. This was also evident from the correlation of the different vanadium phases for pure and composite catalysts with their respective catalytic results. Both polymeric and monomeric vanadium species on an SnO2 surface proved to be critical for the high catalytic performance of the catalyst. The high catalytic performance displayed by V2O5/SnO2 can provide opportunities for further development as a green and economical protocol for direct phenol synthesis from benzene hydroxylation with excellent catalyst recyclability. © 2014 Elsevier B.V. All rights reserved. ction ntinuing interest in the development of highe catalysts with capabilities to achieve efficient ation in green transformation of organic chemicals able carbon-material resources has been one of the es in modern chemical research. These driving factors monstrated by the enormous research interest in the nt of catalysis-mediated phenol production processes he academic and industrial fraternity [1]. Accordingly, phase oxidation (LPO) of benzene to phenol by the on process is one of the important chemical reactions ding author. Fax: +27 12 841 2229. resses: pmakgwane@csir.co.za, makgwane.peter@gmail.com e), rsuprakas@csir.co.za (S.S. Ray). in the oxyfunctionalization of aromatic hydrocarbons, which occurs via the activation of the inert C H bonds in benzene for the production of oxygenated intermediates [1–4]. Such LPO reactions have previously been performed using waste-generating strong mineral acids (e.g., H2SO4, HNO3, etc.) as oxidants and catalysts, which are now deemed unacceptable [5]. With the recent demand for green and sustainable chemistry-processing protocols, it is required that these old methods are being replaced by new environmentally-benign and selective catalytic processes that can utilize abundant atom-efficient and safe oxidants, such as molecular oxygen (O2) and hydrogen peroxide (H2O2), under mild

LPO reaction conditions. Thus, this technological shift in solid heterogeneous catalytic oxidation reactions presents advantageous processes that can be performed under mild reaction conditions.

These processes generate minimal waste due to simple catalyst recovery from the reaction products, thus mitigating the environmental impact [6]. Moreover, the current industrial production of rg/10.1016/j.apcata.2014.12.024 2014 Elsevier B.V. All rights reserved.pment of a high-performance nanostru t for efficient benzene hydroxylation akgwanea,∗, Suprakas S. Raya,b,∗ ional Centre for Nanostructured Materials, Council for Scientific and Industrial Researc f Applied Chemistry, University of Johannesburg, Doornfontein 2028, South Africa e i n f o ugust 2014 a b s t r a c t

Nanostructured vanadium-tin oxide ( been synthesized. The V2O5/SnO2 nanred V2O5/SnO2 oria 0001, South Africa

SnO2) catalysts with V2O5 loading in a range of 5–20 wt% have ctures exhibited effective catalytic performance in the hydroxP.R. Makgwane, S.S. Ray / Applied Catalysis A: General 492 (2015) 10–22 11 phenol is based on the complex multistep non-catalyzed Hock LPO process using cumene [1,7]. Ideally, the Hock process involves the preparation of cumene by the iso-propylation of benzene followed by its oxidation to cumylhydroperoxide (CHP) and the subsequent decomposit phenol that several orga application nomically c compared t successful i process sig recyclable, based on su of an efficie to be a ch catalysis co designing a coverages r to study it reaction. In

V2O5 provi of such sust

To date cessfully ex hydroxylati vanadium-b dium phosp [28–30], ha complexes

However, th to stabilize trial applica present the issues of m mance of th design of ca ity to active for benzene multi-vanad effective ac dation of b a simple V2 played 100