Ni-Pd/γ-Al2O3 Catalysts in the Hydrogenation of Levulinic Acid and Hydroxymethylfurfural towards Value Added Chemicals

Emilia Soszka,Marcin Jędrzejczyk,Agnieszka Ruppert,Nicolas Keller,Ireneusz Kocemba

doi:10.3390/catal10091026

Abstract

γ-Al2O3 supported Ni-Pd catalysts with different Ni:Pd ratios were studied in the hydrogenation of two industrially-relevant platform molecules derived from biomass, namely levulinic acid and hydroxymethylfurfural. The bimetallic catalysts showed better performances in both processes in comparison to the monometallic counterparts, for which a too strong interaction with the alumina support reduced the activity. The behavior of the bimetallic catalysts was dependent on the Ni:Pd ratio, and interestingly also on the targeted hydrogenation reaction. The Pd-modified Ni-rich system behaves like pure Ni catalyst, but with a strongly boosted activity due to a higher number of Ni active sites available, Pd being considered as a spectator. This high activity was manifested in the levulinic acid hydrogenation with formic acid used as an internal hydrogen source. This behavior differs from the case of the Pd-rich system modified by Ni, which displayed a much higher Pd dispersion on the support compared to the monometallic Pd catalyst. The higher availability of the Pd active sites while maintaining a high surface acidity allows the catalyst to push the HMF hydrodeoxygenation reaction forward towards the green biopolymer precursor 2,5-bis(hydroxymethyl)-tetrahydrofuran, and in consequence to strongly modify the selectivity of the reaction. In that case, residual chlorine was proposed to play a significant role, while Ni was considered as a spectator.

Highlights

Biomass is considered as a very promising feedstock due to its abundance and availability.In particular, lignocellulosic waste materials have recently undergone extensive research in the field of renewable and sustainable resources for the industrial production of high-value chemicals and liquid fuels [1,2]
Furfural was achieved over the bimetallic Ni-Pd/SiO2 catalyst, and the key role played by the alloy was hypothesized. When it comes to levulinic acid (LA) hydrogenation with formic acid (FA) as a hydrogen source reaction, we demonstrated recently that among the noble metal dopants (Pt, Pd, Ru, Rh) of Ni catalyst, Pd was the most active, and preliminary results showed that the activity of the bimetallic Ni−Pd catalysts could be tuned depending on the preparation method [18]
In addition to the diffraction peaks corresponding to the γ-Al2 O3 support, only broad peaks/shoulders revealed the presence of metallic Ni for the 4% Ni catalyst; they were further attenuated upon the addition of 1% Pd in the bimetallic 4%Ni-1%Pd sample, while not visible in the low Ni loading (1%) bimetallic counterpart sample

Summary

Introduction

Biomass is considered as a very promising feedstock due to its abundance and availability.In particular, lignocellulosic waste materials have recently undergone extensive research in the field of renewable and sustainable resources for the industrial production of high-value chemicals and liquid fuels [1,2]. Two of the most promising intermediates (platform molecules) that can be derived from the hydrolysis of cellulose, and in particular from the dehydration of C-6 carbohydrates, are hydroxymethylfurfural (HMF), considered as an appealing starting material for various chemical synthesis owing to both its furan ring and the presence of two functional groups, as well as levulinic acid (LA). Their further hydrogenation enables the synthesis of high value-added molecules (Scheme 1, indicating the notations used here).

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