On the Role of Protonic Acid Sites in Cu Loaded FAU31 Zeolite as a Catalyst for the Catalytic Transformation of Furfural to Furan.

Łukasz Kuterasiński,Joanna Kaim,Dorota Rutkowska-Zbik,Małgorzata Zimowska,Katarzyna Samson,Wojciech Rojek,Mariusz Gackowski,Małgorzata Smoliło-Utrata,Jerzy Podobiński,Dorota Duraczyńska

doi:10.3390/molecules26072015

Abstract

The aim of the present paper is to study the speciation and the role of different active site types (copper species and Brønsted acid sites) in the direct synthesis of furan from furfural catalyzed by copper-exchanged FAU31 zeolite. Four series of samples were prepared by using different conditions of post-synthesis treatment, which exhibit none, one or two types of active sites. The catalysts were characterized by XRD, low-temperature sorption of nitrogen, SEM, H2-TPR, NMR and by means of IR spectroscopy with ammonia and CO sorption as probe molecules to assess the types of active sites. All catalyst underwent catalytic tests. The performed experiments allowed to propose the relation between the kind of active centers (Cu or Brønsted acid sites) and the type of detected products (2-metylfuran and furan) obtained in the studied reaction. It was found that the production of 2-methylfuran (in trace amounts) is determined by the presence of the redox-type centers, while the protonic acid sites are mainly responsible for the furan production and catalytic activity in the whole temperature range. All studied catalysts revealed very high susceptibility to coking due to polymerization of furfural.

Highlights

Furan is a heterocyclic organic compound whose molecule consists of a five membered aromatic ring formed by four carbon and one oxygen atoms
Direct synthesis of furan from furfural was catalyzed both by copper-exchanged and copper-free dealuminated faujasite type zeolite
Brønsted acid sites were mainly responsible for the catalytic activity in the whole temperature range

Summary

Introduction

Furan is a heterocyclic organic compound whose molecule consists of a five membered aromatic ring formed by four carbon and one oxygen atoms. It is a precious precursor, mainly used in the production of chemicals such as α-acetylfuran, 2,2-difurylpropane, pyrrole derivatives and many other compounds [1]. Furan may be produced using 1,3-butadiene or furfural as substrates. The first option is a partial oxidation of 1,3-butadiene in the vapor phase at 500 ◦ C over MoO3 and WO3 catalysts, the obtained furan yields are very poor (10–15%) in spite of utilization of promoters such as Mo, Ni and Co [1]. More straightforward way is a direct decarbonylation of furfural with a release of a molecule of carbon monoxide (see Figure 1 [3]), the process that may be treated as a side reaction during the hydrogenation of furfural [3,4]

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