Abstract Energy and the environment will always play key roles in society. The climate emergency cannot be ruled out to enable the transition for a clean energy future. Currently, non-renewable energy resources are declining, therefore is important to continuously explore renewable resources. Biomass is a renewable resource that can be applied to reduce climate changes and to accomplish emission policies. Cellulose is the most abundant type of biomass worldwide, which can be transformed into biofuels and potential building block platform molecules (e.g furfural) throughout biological or chemical methods. Furfural can be synthetized from cellulose using hydrolysis and dehydration reactions. Furfural has a furan ring and carbonyl functional group which makes it an important intermediary to produce higher value-added molecules at industrial level. These molecules include gasoline, diesel and jet fuel. However, furfural can also be transformed by hydrogenation, oxidation, decarboxylation and condensation reactions. The selective hydrogenation of furfural produces furfuryl alcohol, an important industrial compound, which is widely employed in the production of resins, fibers, and is considered an essential product for pharmaceutical applications. On the other hand, the oxidation of furfural produces furoic acid which is applied in the agrochemical industry, where it is commonly transformed to furoyl chloride which is finally used in the production of drugs and insecticides. The oxidation and reduction of furfural can carry out through heterogeneous and homogeneous catalysis, and biocatalysis, etc. Selectivity is an important issue in furfural hydrogenation and oxidation reactions since different products can be obtained by using monometallic or bimetallic catalysts and/or different catalyst supports. In biocatalysis approach, different enzymes, complete cells, tools of modern biotechnology, DNA sequencing, regulation of metabolic networks, overexpression of genes that encode enzymes of interest and optimization of the cellular properties of the microorganism are used. To degradate furanic compounds, improving the productivity and selectivity on a target compound. Herein, a review on the current status of furfuryl alcohol and furoic acid production from furfural by heterogeneous catalysis and biocatalysis has been studied. The stability, selectivity and activity of catalysts along with the different furfural oxidation and reduction conditions have been pointed out. Additionally, the main enzymes, microorganisms and mechanism involved in the furfural degradation process have also been discussed.

RESUMO O desenvolvimento dos processos de produção de nanotubos de carbono é amplamente estudado com o objetivo de melhorar a produção, pureza e qualidade do produto. Entre os processos de produção de nanotubos, a deposição química em fase vapor sobre catalisadores é o método mais empregado para produção em larga escala, pois este permite controlar, de modo eficiente, os parâmetros reacionais. Catalisadores de CoMo/MgO com baixa concentração de cobalto, 5% em massa, e três diferentes concentrações de molibdênio, 5, 10 e 20%, foram preparados pelo método de impregnação seca para estudar o efeito do molibdênio na síntese de nanotubos de carbono. As caracterizações dos catalisadores e dos nanotubos puderam demonstrar as relações entre as propriedades catalíticas e as características dos nanotubos. Os catalisadores com maior concentração de molibdênio apresentaram maior formação de espécies CoMoO4 e MgMoO4 indicando maior interação do cobalto e do suporte com o molibdênio. A elevada concentração de molibdênio nos catalisadores prejudicou a taxa de formação dos nanotubos e a menor grau de grafitização.

ABSTRACT The development of carbon nanotubes production has been subject of research seeking higher carbon yields and selective processes towards materials with superior purity and quality. Among the methods for nanotube synthesis, the catalytic route is a viable option for large-scale production, since it allows a more effective control of reaction. CoMo/MgO catalysts with low loading of cobalt, 5 wt.%, and three different loading of molybdenum, 5, 10 and 20 wt.%, were prepared by incipient wetness impregnation for high yield and pure carbon nanotubes. A detailed characterization of the catalysts and nanotubes indicated a relationship between their properties. Catalysts prepared with higher molybdenum loading showed higher formation of MgMoO4 and CoMoO4 indicating an enhanced interaction of MgO and cobalt with molybdenum. Excess of molybdenum in the catalyst caused a decrease in carbon yield and produced nanotubes with a lower degree of graphitization.

Abstract CoMo/MgO catalysts with low loading of cobalt and molybdenum were prepared by incipient wetness impregnation and the sol-gel method for high yield production of carbon nanotubes (CNT). A detailed characterization of the catalysts, as-produced CNT and purified CNT, indicated a relationship between carbon nanotube properties, synthesis and purification steps. Excess of molybdenum in the catalyst caused a decrease in carbon yield and produced CNT with a lower degree of graphitization. Catalysts prepared by the sol-gel method and with higher molybdenum loading showed an improved interaction between cobalt and molybdenum, increasing the formation of CoMoO4, which was not completely removed during the purification step. The purification removed all MgO and part of the cobalt and molybdenum present in samples without significant damage to the CNT structure. An increase in sample purity could be achieved by increasing reaction time.