Here, we present the low-temperature (∼600 °C) solution combustion method for the fabrication of CoFe2O4, NiFe2O4, and Co0.5Ni0.5Fe2O4 nanoparticles (NPs) of 12–64 nm range in pure cubic spinel structure, by adjusting the oxidant (nitrate ions)/reductant (glycine) ratio in the reaction mixture. Although nitrate ions/glycine (N/G) ratios of 3 and 6 were used for the synthesis, phase-pure NPs could be obtained only for the N/G ratio of 6. For the N/G ratio 3, certain amount of Ni2+ cations was reduced to metallic nickel. The NH3 gas generated during the thermal decomposition of the amino acid (glycine, H2NCH2COOH) induced the reduction reaction. X-ray diffraction (XRD), Raman spectroscopy, vibrating sample magnetometry, and X-ray photoelectron spectroscopy techniques were utilized to characterize the synthesized materials. XRD analyses of the samples indicate that the Co0.5Ni0.5Fe2O4 NPs have lattice parameter larger than that of NiFe2O4, but smaller than that of CoFe2O4 NPs. Although the saturation magneti...

Structural, Magnetic, and Catalytic Evaluation of Spinel Co, Ni, and Co-Ni Ferrite Nanoparticles Fabricated by Low-Temperature Solution Combustion Process.

A combination of ethanol solvent and hydrotalcite (HT) with a Mg/Al ratio of 3:1 was effective for the isomerization of glucose to fructose in up to 56% yield with a high selectivity of 80%. The ethanol solvent shifts the isomerization equilibrium between glucose and fructose, which allows the fructose yield to exceed the upper limit of enzymatic isomerization conducted in water at modest temperatures (i.e., 50%). The HT catalyst maintained such high catalytic performance in repeated use at least three times via calcination and subsequent reconstruction of the original layered structure by the memory effect, which was operated in an aqueous solution containing ammonium carbonate. The results of catalyst screening, characterization, and isotope tracer analysis have revealed that the base sites of HT mainly contribute to its high catalytic activity for glucose-to-fructose isomerization.

Selective Glucose-to-Fructose Isomerization in Ethanol Catalyzed by Hydrotalcites

Catalytic oxidation conversion of biomass-derived resource to high value-added products has evoked considerable interest. Herein, we report a Pt atomic clusters catalyst (size: 1.3 nm) supported on rehydrated layered double hydroxides (denoted as Pt/re-Mg4Al-LDHs), which exhibits great catalytic behavior towards selective oxidation reaction of furfural to furoic acid (conversion: 99 %; yield: 97 %; reaction rate: 676.57 mmol gPt−1 h−1). This result stands at the highest standard compared with reported Pt-based catalysts. A combination research confirms the formation of surface Ptδ− species, due to the local electron transfer from support to Pt atomic clusters. LDHs provide a confined effect to achieve tunable size and highly-stabilized metal clusters, which imposes influence on catalytic performance via metal-support interactions. Both experimental methods (In situ DRIFTS, Raman, EPR and Isotope Labelling MS) and theoretical calculations reveal that the negatively-charged Pt active site plays a crucial role in determining catalytic behavior: C O bond undergoes activation adsorption on Ptδ− site, followed by reaction with H2O (Aldehyde-Water Shift); subsequently, oxygen is activated to generate reactive oxide species (O2−) that serves as a hydrogen acceptor (Oxidative Dehydrogenation) to produce furoic acid. This work displays a valuable paradigm for preparation of noble metal atomic clusters catalysts based on memory effect of LDHs support, which would pave a way for the development of heterogeneous catalysts toward selective oxidation reactions.

Pt atomic clusters catalysts with local charge transfer towards selective oxidation of furfural

The parameters governing the basic reactivity of kadox and ex-carbonate zinc oxide samples towards alcohol conversion were investigated varying the atmosphere of pre-treatment for a model reaction, the methylbutynol (MBOH) conversion, and the ethanol conversion reaction, a transformation of potential higher industrial impact. The catalytic properties of ZnO can thus be tuned: enhanced activities were measured after a pre-treatment performed under inert gas as compared to oxidative conditions. If no significant variation of residual hydroxylation nor carbonation can account for this behaviour, a quantitative correlation between the variation of MBOH conversion induced by the different atmosphere of pre-treatment with that of the concentration in oxygen vacancies characterized by in situ EPR found, showing that oxygen vacancies play a key role towards basic reactivity. In fact, the electronic density of the oxygen of the active acid/base pair is directly influenced by the electron release or capture associated to the formation or filling up of oxygen vacancies, respectively. On the kadox samples, the presence of an additional weaker active site is responsible for the residual activity of kadox sample in the absence of oxygen vacancies. The existence and location on specific crystallographic faces of these sites are discussed in relation with the different morphologies of the two samples and with their different affinity with CO2. Even if the occurrence of oxygen vacancies still governs the conversion level for ethanol transformation, the reactivity inhibition after oxidative pre-treatment is less pronounced due to the higher reaction temperature that limits the efficiency of oxygen vacancies filling-up under oxidative atmospheres. The nature of active sites leading to the formation of acetaldehyde and ethylene is also discussed.

Role of oxygen vacancies in the basicity of ZnO: From the model methylbutynol conversion to the ethanol transformation application

Promotion effect of coexistent hydromagnesite in a highly active solid base hydrotalcite catalyst for transesterifications of glycols into cyclic carbonates

Solid Base Catalysis

Hydrotalcite and related materials are very important catalysts and catalyst precursors. The synthesis, structure and catalytic application of hydrotalcite have been reviewed by several authors.1–3) The catalytic aspects of hydrotalcite have also been reviewed.4,5)

Preparation and Catalytic Properties of Solid Base Catalysts — II. Specific Materials for Solid Bases

In order to predict the capability of solid surface as base catalysts, the basic properties of the surfaces must be clarified. The basic character or basicity includes the following factors: a) the number of basic sites, b) the origin or location of basic sites, and c) the base strength of basic sites.

Characterization of Solid Base Catalysts

MgO, CaO, SrO and BaO are representative solid base catalysts that are used for a number of base-catalyzed reactions. The surface basic strength is believed to follow the order: MgO < CaO < SrO < BaO. Among these, MgO has been studied most extensively, probably because samples of definite structure with high surface area are prepared much more easily by thermal pretreatment than samples of CaO, SrO and BaO. The structures of CaO, SrO, and BaO are similar to that of MgO, and thus, the catalytic and surface properties of CaO, SrO, and BaO can be estimated from the results obtained with MgO. Although BeO and RaO are included in the alkaline earth oxides, they have not been studied because of toxicity and radioactivity, respectively.

Preparation and Catalytic Properties of Solid Base Catalysts — I. Metal Oxides

In 1958, Pines and Haag reported that when sodium dispersed on powdered alumina (8 wt%) was used as a catalyst, double bond isomerization of 1-butene proceeded at 310 K.1) The ratio of cis/trans was much greater than that of the thermo dynamic equilibrium mixture. In contrast to the well-known acid-catalyzed isomerization proceeding through carbenium ions, no rearrangements of the carbon skeleton were observed in the base-catalyzed reactions, indicating the anionic nature of the intermediate. This was the first report on solid base catalysis.

Yoshio Ono

Papers

Solid Base Catalysis

Preparation and Catalytic Properties of Solid Base Catalysts — II. Specific Materials for Solid Bases

Characterization of Solid Base Catalysts

Preparation and Catalytic Properties of Solid Base Catalysts — I. Metal Oxides

Reactions Catalyzed by Solid Bases