Tailoring acidity and porosity of alumina catalysts via transition metal doping for glucose conversion in biorefinery

Gas-Phase Mechanism of O.- /Ni2+ -Mediated Methane Conversion to Formaldehyde

The gas-phase reaction of NiAl₂ O₄ ⁺ with CH₄ is studied by mass spectrometry in combination with vibrational action spectroscopy and density functional theory (DFT). Two product ions, NiAl₂ O₄ H⁺ and NiAl₂ O₃ H₂ ⁺ , are identified in the mass spectra. The DFT calculations predict that the global minimum-energy isomer of NiAl₂ O₄ ⁺ contains Ni in the +II oxidation state and features a terminal Al-O^.- oxygen radical site. They show that methane can react along two competing pathways leading to formation of either a methyl radical (CH₃ ⋅) or formaldehyde (CH₂ O). Both reactions are initiated by hydrogen atom transfer from methane to the terminal O^.- site, followed by either CH₃ ⋅ loss or CH₃ ⋅ migration to an O^2- site next to the Ni²⁺ center. The CH₃ ⋅ attaches as CH₃ ⁺ to O^2- and its unpaired electron is transferred to the Ni-center reducing it to Ni⁺ . The proposed mechanism is experimentally confirmed by vibrational spectroscopy of the reactant and two different product ions.

N-Doped natural albite mineral as green solid catalyst for efficient isomerization of glucose into fructose in water

A green and effiecient N-doped mineral catalyst (i.e., CS/Ab) prepared by biomass waste and natural albite was explotied for glucose-to-fructose isomerization.

Recent Advances in the Brønsted/Lewis Acid Catalyzed Conversion of Glucose to HMF and Lactic Acid: Pathways toward Bio-Based Plastics

One of the most trending topics in catalysis recently is the use of renewable sources and/or non-waste technologies to generate products with high added value. That is why, the present review resumes the advances in catalyst design for biomass chemical valorization. The variety of involved reactions and functionality of obtained molecules requires the use of multifunctional catalyst able to increase the efficiency and selectivity of the selected process. The use of glucose as platform molecule is proposed here and its use as starting point for biobased plastics production is revised with special attention paid to the proposed tandem Bronsted/Lewis acid catalysts.

Natural mineral bentonite as catalyst for efficient isomerization of biomass-derived glucose to fructose in water

The development of inexpensive and efficient heterogeneous catalyst for the conversion of biomass including food and winery processing waste to value-added products is crucial in biorefinery. Glucose could be obtained via the hydrolysis of waste cellulose or starch-rich material, and the isomerization of glucose to fructose using either Lewis acid or Brønsted base catalysts is an important route in biorefinery. As a natural clay mineral, bentonite (Bt) is widely used as adsorption material and catalyst support, but how its intrinsic acid-base properties can impact the biomass conversion chemistry is still rarely reported. In this study, we investigated the influence of the textural and acid-base properties of Bt on the glucose isomerization reaction. The reaction kinetics and mechanism, and the effect of Al³⁺-exchange were explored. The results showed that the activation energy of Bt-catalyzed glucose conversion was 59.0 kJ mol^-1, and the in-situ Fourier transform infrared spectrometer (FT-IR) characterization proved that Brønsted base was responsible for the isomerization. The highest fructose yield of 39.2% with 86.3% selectivity could be obtained at 110 °C for 60 min in water. Alkaline rinse and calcination can recover most of the catalytic activity of the spent catalyst.

Microwave-assisted liquefaction of carbohydrates for 5-hydroxymethylfurfural using tungstophosphoric acid encapsulated dendritic fibrous mesoporous silica as a catalyst

Tungstophosphoric acid (TPA) encapsulated dendritic fibrous silica KCC-1 was prepared via a microemulsion system with the simple reflux method using cetyltrimethylammonium bromide as a structure-directing agent. The TPA impregnated on KCC-1 (ITPA-KCC-1) was also prepared for comparative. Various physicochemical techniques were used to characterize the synthesized materials and their activity evaluated in the 5-hydroxymethylfurfural (HMF) formation from carbohydrates derivatives of fructose, glucose and cellulose. The effect of various factors such as catalyst to substrate ratio, different solvents and temperature were investigated on the formation of HMF. The resultant encapsulated catalyst was very active in fructose dehydration with the yield of 92% HMF and full conversion of fructose at 120 °C for 30 min under the microwave heating condition without any salt additive in the THF solvent system as well as 95% in MIBK solvent. The HMF yield was achieved by 58% and 16.2% from glucose and cellulose in the DMSO solvent, respectively. The TPA-KCC-1 can be separated easily after reaction from the reaction mixture and reused atleast five times without substantial loss in catalytic activity. This study provides an easy encapsulation method for TPA in dendritic fibrous silica KCC-1 as a heterogeneous catalyst, and it should have great application potential in other biomass valorization processes.