Effect of Activation Methods of Molecular Sieves on Ketimine Synthesis

Although the use of molecular sieves for imine synthesis is a common protocol, there have been no comprehensive studies on heat-drying methods. This can be crucial for reproducibility. It was found that molecular sieve 5A dried at 160 °C for 5 h under vacuum efficiently promoted the condensation of various ketones and amines to afford even relatively bulky ketimines. Several control experiments and analyses revealed that only a small amount of Brønsted acid sites was important for the activity, rather than dehydration ability. Other types of molecular sieves could be utilized for the reaction after treatment with water followed by heat drying. A continuous-flow acetalization reaction of alcohols using the activated molecular sieve 5A was also demonstrated.

High catalytic activity of CuY catalysts prepared by high temperature anhydrous interaction for the oxidative carbonylation of methanol

CuY catalysts were prepared by high temperature anhydrous interaction between NH₄Y zeolite and copper(ii) acetylacetonate Cu(acac)₂ and the activities were measured for the oxidative carbonylation of methanol to dimethyl carbonate under atmospheric pressure. The bulk and surface properties of the as-prepared catalyst were characterized by XRD, H₂-TPR and XPS techniques. The activation atmosphere of the CuY catalyst and the testing temperature of the catalytic activity was systematically studied. During activation, nitrogen promotes the auto-reduction of Cu²⁺ to form the Cu⁺ active center, but deposited carbon on the surface of the CuY catalyst covers the active center, even plugging the channel, resulting in lower catalytic activity. Oxygen eliminates deposited carbon, but is not so good for the auto-reduction of Cu²⁺. Nitrogen doped with a small amount of oxygen not only eliminates the deposited carbon, but also promotes the auto-reduction of Cu²⁺ to form more Cu⁺ active centers. With the testing temperature increasing, the catalytic activity increases first and then decreases. When the testing temperature is 170 °C, the CuY catalyst with satisfactory activity and stability showed an excellent catalytic activity with 525.1 mg g⁻¹ h⁻¹ space time yield of DMC (STY_DMC) and 18.9% methanol conversion. Then the longevity was investigated at 170 °C for 150 h. During the initial reaction period of 40 h, the STY_DMC value was constant. In the next 20 h, the catalytic activity slightly decreased. But in the last 90 h, the catalytic performance is very stable and the STY_DMC value remains 480 mg g⁻¹ h⁻¹. The main cause of deactivation is the growth of the particles.

The CuY catalysts prepared by high temperature anhydrous interaction were activated under different atmospheres and the activities were measured for the oxidative carbonylation of methanol to dimethyl carbonate under atmospheric pressure.

Plasma impact on structural, morphological and optical properties of copper acetylacetonate thin films

The influence of plasma exposure on structural, morphological and optical properties of copper (II) acetylacetonate thin films deposited by thermal evaporation technique was investigated. Copper (II) acetylacetonate as-grown thin films were exposed to the atmospheric plasma for different times. The exposure of as-grown cu(acac)₂ thin film to atmospheric plasma for 5min modified its structural, morphological and optical properties. The effect of plasma exposure on structure and roughness of cu(acac)₂ thin films was evaluated by XRD and AFM techniques, respectively. The XRD results showed an increment in crystallinity due to exposure for 5min, but, when the exposure time reaches 10min, the film was transformed to an amorphous state. The AFM results revealed a strong modification of films roughness when the average roughness decreased from 63.35nm to ~1nm as a result of interaction with plasma. The optical properties of as-grown and plasma exposured cu(acac)₂ thin films were studied using spectrophotometric method. The exposure of cu(acac)₂ thin films to plasma produced the indirect energy gap decrease from 3.20eV to 2.67eV for 10min exposure time. The dispersion parameters were evaluated in terms of single oscillator model for as-grown and plasma exposured thin films. The influence of plasma exposure on third order optical susceptibility was studied.

Efficient electrochemical transformation of CO2 to C2/C3 chemicals on benzimidazole-functionalized copper surfaces

Benzimidazole (BIMH)-modified copper foil enhances the selective conversion of CO₂ to C₂/C₃ products via providing highly active H^δ+.