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2,5‐dimethylfuran (DMF) is a promising compound in the production of biofuel with high‐quality properties. In this study, it is aimed to develop new efficient catalysts to synthesize DMF from 5‐hydroxymethylfurfural (HMF). Co, Mn/Co, and Ru/Co catalysts were prepared using the NaBH4 reduction method. The catalysts were subjected to activity tests for the hydrogenation of HMF to DMF by changing the reaction parameters, such as temperature and time. Mn/Co catalysts prepared from metal precursors at various molar ratios of Mn/Co were found to be effective in hydrogenation reactions of HMF to DMF. A 91.8% DMF yield was achieved in the presence of a Mn/Co (50/50) catalyst without noble metal at 180°C for 4 hours. The Brunauer‐Emmet‐Teller (BET) method, x‐ray diffraction (XRD), x‐ray photoelectron spectroscopy (XPS), and induction coupled plasma mass spectroscopy (ICP‐MS) techniques were used to characterize the efficient Mn/Co catalyst.

IntroductionCyanobacteria are photosynthetic bacteria that use sunlight as an energy source, water as an electron donor, and carbon dioxide as a carbon source to produce food. They use oxygen to support life and usually live in fresh or marine water. They produce organic material and thus they are known as primary producers (Ozturk Urek and Tarhan, 2011;Tian et al., 2014). The cyanobacterium Spirulina platensis is a filamentous, nitrate-utilizing, nonnitrogenfixing, photosynthetic organism that is rich in pigments such as chlorophyll a, carotenoids, and phycobiliproteins. These properties make it very important in nutritional, industrial, and environmental biotechnology (Tarko et al., 2012). It is a healthy food and also has defensive properties against viral diseases and anemia. It is used as a colorant because of its rich pigment content (Henrikson, 2010;Singh et al., 2014). Antioxidant properties and the high vitamin, protein, carbohydrate, and mineral values of S. platensis inhibit tumor growth and malnutrition. S. platensis is rich in protein content and contains 60%-70% protein by dry weight (Jha et al., 2007), including 9 essential amino acids that are considered high-quality protein (Belay, 2008). Nitrogen is an essential element due to nitrogen assimilation or incorporation of the most important functional and structural macromolecules in organisms, such as amino acids. Nitrogen is the most important element due to its approximately 10% contribution to cyanobacterium cells (Perez-Garcia et al., 2011), with 15% of this rate composed of incorporated proteins and nucleic acids (Inokuchi et al., 2002).Minerals are the other vital members involved in the growth and enzymatic activities of S. platensis (Tarko et al., 2012). The growth and metabolic activity of cyanobacteria may be limited by a variety of these minerals. They affect the growth and metabolic activity of Spirulina (Ozturk Urek and Tarhan, 2011). One of the most important elements for the growth of Spirulina is iron (Fe). It is a limiting factor for pigment production (chlorophyll a). Investigations into the relationship between chlorophyll a biosynthesis and iron show that iron deficiency causes chlorosis. It decreases chlorophyll a and heme production and represses porphyrin biosynthesis (Belkhodja et al., 1998; Briat et al., 2007; Reinbothe et al., 2010). Additionally, Fe is a significantly important element for nitrogen assimilatory enzymes. The structures of the enzymes consist of Fe as cofactor. Cubic clusters of Fe and

The effect of various concentrations of ammonium nitrate (5-60 mM), an economical nitrogen source, on the growth, nitrate-ammonium uptake rates, production of some pigments and metabolites, and some nitrogen assimilation enzymes such as nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT) in Spirulina platensis (Gamont) Geitler was investigated. Ten millimolars of ammonium nitrate stimulated the growth, production of pigments and the other metabolites, and enzyme activities, whereas 30 and 60 mM ammonium nitrate caused inhibition. In the presence of 10 mM ammonium nitrate, different concentrations of iron were tried in the growth media of S. platensis. After achieving the best growth, levels of metabolite and pigment production, and enzyme activities in the presence of 10 mM ammonium nitrate as a nitrogen source, different iron concentrations (10-100 µM) were tried in the growth medium of S. platensis. The highest growth, pigment and metabolite levels, and enzyme activities were determined in the medium containing 50 µM iron and 10 mM ammonium nitrate. In this optimum condition, the highest dry biomass level, chlorophyll a, and pyruvate contents were obtained as 55.42 ± 3.8 mg mL(-1) , 93.114 ± 7.9 µg g(-1) , and 212.5 ± 18.7 µg g(-1) , respectively. The highest NR, NiR, GS, and GOGAT activities were 67.16 ± 5.1, 777.92 ± 52, 0.141 ± 0.01, and 44.45 ± 3.6, respectively. Additionally, 10 mM ammonium nitrate is an economical and efficient nitrogen source for nitrogen assimilation of S. platensis, and 50 µM iron is optimum for the growth of S. platensis.

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