Excess soluble alkalis to prepare highly efficient MgO with relative low surface oxygen content applied in DMC synthesis

The activities of various MgO catalysts, which were prepared from different methods such as hydration synthesis, thermal decomposition, combustion, sol–gel and co-precipitation, were conducted in dimethyl carbonate (DMC) synthesis via transesterification of ethylene carbonate with methanol. MgO-P-Na2CO3-3.14 synthesized by the excess Na2CO3 precipitation compared the best catalytic activity and stability, which could be reused for seven times without obvious deactivation. The DMC yield was as high as 69.97% at 68 °C. The transesterification reaction could be separated into two steps, and the samples obtained by NaOH precipitant exhibited better ring-opening capability, while the catalysts acquired by Na2CO3 precipitant displayed superior transesterification ability. The structure-performance relationship was evaluated by multiple characterization methods. The results indicated that the as-synthesized catalyst derived from dried precursors with more crystalline magnesium carbonate was favorable for the promotion of DMC yield, and MgO-P-Na2CO3-3.14 with more Mg-O pairs, which were the active center for the transesterification of 2-hydroxyethyl methyl carbonate (HEMC) intermediate with methanol, resulted in more moderately basic sites left that was in accordance with the DMC yield variation. MgO-P-Na2CO3-3.14 with greater BET surface area and mesopore volume, relative low surface oxygen content and larger moderately basic sites amount compared the excellent activity in DMC synthesis.

Synthesis of Dimethyl Carbonate by Transesterification of Propylene Carbonate with Methanol on CeO2-La2O3 Oxides Prepared by the Soft Template Method

In this study, CeO2, La2O3, and CeO2-La2O3 mixed oxide catalysts with different Ce/La molar ratios were prepared by the soft template method and characterized by different techniques, including inductively coupled plasma atomic emission spectrometry, X-ray diffraction, N2 physisorption, thermogravimetric analysis, and Raman and Fourier transform infrared spectroscopies. NH3 and CO2 adsorption microcalorimetry was also used for assessing the acid and base surface properties, respectively. The behavior of the oxides as catalysts for the dimethyl carbonate synthesis by the transesterification of propylene carbonate with methanol, at 160 °C under autogenic pressure, was studied in a stainless-steel batch reactor. The activity of the catalysts was found to increase with an increase in the basic sites density. The formation of dimethyl carbonate was favored on medium-strength and weak basic sites, while it underwent decomposition on the strong ones. Several parasitic reactions occurred during the transformation of propylene carbonate, depending on the basic and acidic features of the catalysts. A reaction pathway has been proposed on the basis of the components identified in the reaction mixture.

The Catalytic Mechanism of Intercalated Chlorine Anions as Active Basic Sites in Mgal-layered Double Hydroxide for COS Hydrolysis

In order to make clear the role of intercalated anions in layered double hydroxides (LDHs) for catalytic hydrolysis of COS, the adsorption and reaction characteristics of COS over the simple Mg2Al-Cl-LDH model catalyst were studied by both theoretical and experimental methods. Density functional theory (DFT) calculations by CASTEP found that the chloride ions in LDH function as the key Brønsted-base sites to activate the adsorbed H2O with enlarged bond length and angle, facilitate the dissociative adsorption of intermediates including mono-thiocarbonic acid (MTA) and hydrogen thiocarbonic acid (HTA), and participate in the formation of transient states and subsequent hydrogen transfer process with decreased energy barriers during COS hydrolysis. COS hydrolysis will preferentially go through the dissociated intermediates of mono-thiocarbonates (MT) and hydrogen thiocarbonates (HT) with dramatically decreased energy barriers, and the rate-determining step of COS hydrolysis over Mg2Al-Cl-LDH will be the nucleophilic addition of C=O in COS by H2O (Ea = 1.10 eV). The experimental results further revealed that the apparent activation energy (0.89 eV) of COS hydrolysis over Mg2Al-Cl-LDH is close to theoretical value (1.10 eV), and the accumulated intermediates of MT, HT or carbonate were also observed by FT-IR around 1363 cm-1 on the used Mg2Al-Cl-LDH, which are well in accordance with the theoretical prediction. The demonstrated participation of intercalated chlorine anions in the evolution of intermediates and transient states as Brønsted-base sites during COS hydrolysis will give new insight into the basic sites in LDH materials.

Graphene oxide and graphite oxide used as reinforcement in composites synthesized from cellulose acetate and polyacrylic acid

This work focused on the synthesis and characterization of composites, obtained based on polyacrylic acid and cellulose acetate, which incorporated graphite oxide and graphene oxide as structural reinforcement. The composites were obtained using the phase inversion method and the incorporation of the reinforcement, during the synthesis process, was carried out in proportions of 1% by weight. The characterization of the composites was carried out using IR, Raman, BET, SEM spectroscopy techniques and methods for determining acidic and basic sites. The results obtained showed that it is possible to synthesize composites that present a network configuration, made up of layers that give the material the effect of depth. Furthermore, it was possible to observe that both graphite oxide and graphene oxide were deposited on the outer edge of the hexagonal pores present in the material. Finally, the concentration values of acidic and basic sites were obtained. The presence of these sites could be associated with carboxylic groups inserted during the oxidation of graphitic materials and with non-reactive sites present in cellulose.

Effects of calcination temperature on the catalyst performance in a CO2 hydrogenation reaction

Cu/ZnO catalysts were synthesized on Al2O3-ZrO2 support via impregnation method with addition of manganese and niobium promoters. Samples were calcined at 181, 350 and 518 ºC. Different characterization techniques such as H2-TPR and CO2-TPD were used to study the catalytic reduction behavior and catalytic basicity, respectively. H2-TPR studies shows that all the catalysts reduction occurred on the range of temperature between 237 ºC and 265 ºC. The CO2-TPD profiles showed that the calcination temperature significantly influences the basicity of the catalyst and the catalyst calcined at 35 0oC was proved to contain the highest amount of the basic sites. Furthermore, the characterization results were validated through analyzing of the catalyst performance during CO2 hydrogenation reaction and the results indicate that highest methanol yield of 12.2 % were obtained from the catalyst that calcined 350 oC.