Kwang Deog Jung

Synthesis and catalytic application of mesoporous molecular sieves MCM-41 containing niobium and tantalum

Niobium- and tantalum-containing mesoporous molecular sieves MCM-41 have been synthesized, and applied as a catalyst for vapor phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam. NbMCM-41 catalyst exhibited high catalytic performance in the vapor phase Beckmann rearrangement of cyclohexanone oxime. The oxime conversions were almost 100% and the lactam selectivities were around 80%. The lactam selectivities of NbMCM-41 catalyst were higher than those of AlMCM-41 catalyst. However, TaMCM-41 catalyst exhibited lower catalytic performance than AlMCM-41 catalyst, and it was fast deactivated with time. These results may be due to the acidity difference among the catalysts. The results from NH3-TPD showed that NbMCM-41 catalyst possessed weak and medium acid sites, while TaMCM-41 catalyst possessed only very weak acid sites. AlMCM-41 catalyst also exhibited only weak acid sites.

Effect of potassium addition on bimetallic PtSn/θ-Al2O3 catalyst for dehydrogenation of propane to propylene

PtSn/θ-Al2O3 catalysts with different amounts of K (0.14, 0.22, 0.49, 0.72, and 0.96xa0wt%) are prepared to investigate the K effects on the PtSn catalyst in propane dehydrogenation (PDH). KPtSn catalyst with 0.xxxa0wt% K, 0.5xa0wt% Pt and 0.75xa0wt% Sn is designated as xx-KPtSn. PDH was performed at 873xa0K and a gas hourly space velocity (GHSV) of 53,000xa0mL/gcatxa0h. The temperature-programmed desorption (NH3-TPD), temperature-programmed reduction (TPR) and CO chemisorption of the KPtSn catalysts with K added revealed the potassium addition blocked the acid sites, promoted the reduction of Sn oxide and decreased the Pt dispersion. The formations of cracking products and higher hydrocarbons on acid sites were suppressed by the K effect of blocking the acid sites. In contrast, K addition at more than 0.72xa0wt% rather increased cracking products and the amount of coke, resulting in the severe deactivation of catalysts. The high cracking products on the KPtSn catalysts with the high amount of K should not be related to the acid sites, because the acid sites were monotonously decreased with an increase in the amount of K. Instead, the potassium affected the characteristics of PtSn. The interaction between Pt and Sn could be weakened by enriching the reduced Sn, because the K component promoted the reduction of Sn oxide in the TPR experiments. Therefore, the 14-KPtSn catalyst with the low amount of K exhibits the highest stability and selectivity among the prepared KPtSn catalysts due to the compromise of the advantageous (blocking the acid sites) and bad (weakening the interaction between Pt and Sn) effects of the K addition in PDH.

Effect of Method of Preparation of Cu-Zn-Al Catalysts on DME Synthesis

A series of Cu-Zn-Al catalysts from the precursors with the hydrotalcite-like structure were prepared, and these catalysts admixed with γ-Al2O3 were tested for DME synthesis in a fixed bed flow reactor in a single step. DME synthesis rates were well correlated with the Cu metal surface of the Cu-Zn-Al catalysts in the admixed catalysts, indicating that DME synthesis rates would be controlled by methanol synthesis rates.

Thermochemical Hydrogen Production Using Ni-Ferrite and CH4

Hydrogen production by a 2-step water-splitting thermochemical cycle using metal oxides (ferrites) redox pairs and CH4 have been studied in this experiment. Reactions were performed in a two-step redox cycle in which the ferrites were reacted with CH4 at 700°C–800°C to produce CO, H2 , and various reduced phases (reduction step); these were then reoxidized with water vapor to generate H2 in water-splitting step (oxidation step) at 600°C–700°C. The reduced forms of Ni-Fe2O3, Ni-FeO and Ni-Fe alloy from XRD, showed respectively different reactivity for H2 formation from H2 O. These were oxidized to the ferrite phase to produce H2 in the water-splitting step at 600°C–700°C. In reduction reaction at 800°C, carbon deposition arise on surface of Ni-ferrite due to CH4 decomposition. This reduced phase containing carbon, which reacts with H2 O at 600°C, produce H2 , CO, and CO2 . The amount of H2 evolved using reduced phase containing carbon was much than that of other phase.Copyright