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  • 5588 Chem. Soc. Rev., 2011, 40, 5588–5617 This journal is c The Royal Society of Chemistry 2011

    Cite this: Chem. Soc. Rev., 2011, 40, 5588–5617

    Catalytic conversion of lignocellulosic biomass to fine chemicals and fuels

    Chun-Hui Zhou,*a Xi Xia,a Chun-Xiang Lin,b Dong-Shen Tonga and Jorge Beltraminib

    Received 5th May 2011

    DOI: 10.1039/c1cs15124j

    Lignocellulosic biomass is the most abundant and bio-renewable resource with great potential for

    sustainable production of chemicals and fuels. This critical review provides insights into the state-of

    the-art accomplishments in the chemocatalytic technologies to generate fuels and value-added chemicals

    from lignocellulosic biomass, with an emphasis on its major component, cellulose. Catalytic hydrolysis,

    solvolysis, liquefaction, pyrolysis, gasification, hydrogenolysis and hydrogenation are the major processes

    presently studied. Regarding catalytic hydrolysis, the acid catalysts cover inorganic or organic acids and

    various solid acids such as sulfonated carbon, zeolites, heteropolyacids and oxides. Liquefaction and fast

    pyrolysis of cellulose are primarily conducted over catalysts with proper acidity/basicity. Gasification is

    typically conducted over supported noble metal catalysts. Reaction conditions, solvents and catalysts are

    the prime factors that affect the yield and composition of the target products. Most of processes yield a

    complex mixture, leading to problematic upgrading and separation. An emerging technique is to

    integrate hydrolysis, liquefaction or pyrolysis with hydrogenation over multifunctional solid catalysts to

    convert lignocellulosic biomass to value-added fine chemicals and bio-hydrocarbon fuels. And the

    promising catalysts might be supported transition metal catalysts and zeolite-related materials. There still

    exist technological barriers that need to be overcome (229 references).

    1 Introduction

    The depletion of fossil fuel resources and the resulting adverse

    effects on the global environment and climate are of major

    academic, economic and political concern worldwide.1–3

    As supplies of fossil fuels and related petrochemicals may soon

    be limited, alternative solutions are sought. One alternative is to

    a Research Group for Advanced Materials & Sustainable Catalysis (AMSC), Breeding Base of State Key Laboratory of Green Chemistry Synthesis Technology, College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou, 310032, China. E-mail: catalysis8@yahoo.com.cn, chc.zhou@yahoo.com.cn

    b The School of Chemical Engineering, ARC Centre of Excellence for Functional Nanomaterials, AIBN, The University of Queensland, St. Lucia, QLD 4072, Australia

    Chun-Hui Zhou

    Dr Chun-Hui (Clayton) Zhou is a Professor of Chemical Engineering and Group Leader of the Research Group for Advanced Materials and Sustainable Catalysis (AMSC) at Zhejiang Univer- sity of Technology as well as a Member of the Editorial Board of Applied Clay Science (Elsevier). He worked as a visiting Academic at the ARC Center of Excellence for Func- tional Nanomaterials, AIBN, the University of Queensland in 2006–2007 and as Visiting

    Professor at the Centre for Strategic Nano-fabrication, the University of Western Australia in 2010. His research interests include clay-based materials for miscellaneous applications, sustainable catalysis for fuels and chemicals from biorenewable resources, process intensification and advanced biomaterials.

    Xi Xia

    Xi Xia has been a postgradu- ate under the supervision of Prof. Chun-Hui Zhou in the Research Group for Advanced Materials & Sustainable Catalysis, Zhejiang University of Technology (ZJUT) since September, 2008. He obtained his Bachelor’s Degree in Chemistry from Nanyang Normal University in 2008 and his Master’s degree of Industrial Catalysis at ZJUT in 2011. His research interests are in advanced clay-based materials, catalysts and their

    potential for the catalytic conversion of biomass into liquid fuels and chemicals.

    Chem Soc Rev Dynamic Article Links

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    http://dx.doi.org/10.1039/c1cs15124j http://dx.doi.org/10.1039/c1cs15124j http://dx.doi.org/10.1039/c1cs15124j

  • This journal is c The Royal Society of Chemistry 2011 Chem. Soc. Rev., 2011, 40, 5588–5617 5589

    develop a series of novel chemical processes based on renewable

    feedstocks, typically biomass4 and biomass-derived chemicals.5–7

    Biomass generally refers to organic materials such as wood,

    grass, algae, agricultural crops and their residues and wastes,

    including some animal waste.8 All of these materials originally

    result from biological photosynthesis from readily available

    atmospheric CO2, water and sunlight. Therefore, biomass is a

    sustainable and green feedstock for the production of fuels and

    fine chemicals with net zero carbon emission.

    Biochemically, living systems produce a large number

    of organic molecules such as carbohydrates, fats and oils,

    phospholipids and glycolipids, waxes, steroids, proteins and

    nucleotides. Among them, carbohydrates are the primary

    energy-storage molecules. Carbohydrates are the main struc-

    tural components of the cell walls of plants, in which the

    carbohydrate polymers, namely cellulose and hemicellulose,

    are tightly bound to the lignin.9 Any materials rich in cellulose,

    hemicelluloses, and lignin are commonly referred to as ligno-

    cellulosic biomass.10 For example, wood, bamboo, grass and

    their derived pulp and paper, and agricultural residues like

    corn stover and sugarcane bagasse are typical sources of

    lignocellulosic biomass.

    Lignocellulosic biomass has received intensive attention

    over the past decade. Many studies have shown that ligno-

    cellulosic biomass offers great potential to be used as a renewable

    feedstock in abundance with easy availability.11–14 Fig. 1 displays

    the weight percentage of cellulose, hemicellulouse and lignin in

    some typical biological sources such as pinaster,15 eucalyptus

    globules,15 wheat straw,16 sorghum stalks,17 bamboo18 and

    banana pseudo-stems.19 Generally, most of the lignocellulosic

    biomass contains 35–50% of cellulose, 20–35% of hemi-cellulose,

    and 10–25% of lignin. Clearly, the major component of ligno-

    cellulosic biomass is cellulose. It is estimated that nearly half of

    the organic carbon in the biosphere is present in the form of

    cellulose. Therefore, in the context of processing lignocellulosic

    biomass into fuels and valuable chemicals, the conversion of

    cellulose is of paramount importance and worth being given

    priority.11–14

    The development of the processes to convert lignocellulosic

    biomass to fuels and value-added chemicals, however, remains

    a big challenge. Firstly, the complex chemical composition of

    lignocellulosic biomass makes it difficult to yield target fuels

    and chemicals in a high yield and quality. Comparatively, as

    to the three main components in lignocellulosic biomass,

    the structure of cellulose is the simplest and most ordered.

    Cellulose consists of only anhydrous glucose units, while

    hemicelluloses contain many different sugar monomers. Con-

    sequently, cellulose is crystalline and hemicellulose just has a

    random, amorphous structure. Different from carbohydrate-

    based cellulose and hemicellulose, lignin is a class of complex,

    cross-linked, three-dimensional biopolymers with phenyl-

    propane units with relative hydrophobic and aromatic properties.

    Those differences in the chemical composition and structure in

    lignin, hemicellulose and cellulose lead to their much different

    reactivity. On one hand, for example, the decomposition of lignin

    and hemicellulose is generally easier than that of cellulose.20,21

    In other words, the decomposition and degradation of cellulose is

    the most difficult and energy-consuming step in the conversion of

    lignocellulosic biomass. As a result, to improving the reactivity of

    cellulose is a first critical point. On the other hand, based on

    their different reactivity, it is feasible to separate cellulose and

    hemicellulose from lignin.22,23 Therefore, as reported in the

    literature and discussed below, besides using the natural ligno-

    cellulosic biomass as the reactants, many researchers often choose

    pure cellulose, in particular microcrystalline cellulose, as a model

    of lignocellulosic biomass.

    Over decades, many researchers have endeavored to explore

    the production of fuels and chemicals from cellulose, which

    is representative of lignocellulosic biomass.24,25 A cellulose

    molecule has the generic chemical formula (C6H12O5)n.

    It consists of a skeletal linear polysaccharide, in which glucose-

    based monomer units are jointed together throug