It is well known that V–Mg based complex oxide catalysts show a high activity for the oxidative dehydrogenation of 1-butene (1-C4H8) to buta-1,3-diene (BD). In this study, in order to improve the catalytic performance of V–Mg based complex oxides, we tried to add metal oxide such as Al2O3, Fe2O3, and Co2O3 and carried out the oxidative dehydrogenation (ODH) of 1-C4H8 without and with molecular O2 at 480 °C. The addition of Co2O3 to the V–Mg complex oxides resulted in the highest BD yield of 22.5 % with only lattice oxygen of the catalyst. For continuous production of BD, the ODH under O2 flow was also investigated. The V–Mg–Co catalyst exhibited higher 1-C4H8 conversion (28.5 %) and BD yield (17.5 %) than those of the V–Mg catalyst, and it was indicated that the high reactivity of the lattice oxygen affected the ODH under O2 flow according to the pulse reaction of 1-C4H8 and 18O2.
Catalytic properties of intermetallic compounds for hydrogenation reactions are reviewed focusing on the differences in selectivity compared with monometallic catalysts. Intermetallic compound catalysts were prepared to form single phase particles of the target compound to clarify the specific catalytic properties. Pt3Ti showed higher activity than Pt for H2 activation and ethylene hydrogenation. Various intermetallic compounds were found to be more selective than monometallic catalysts for the partial hydrogenation of alkyne into alkene. RhBi showed regioselectivity for the terminal C = C hydrogenation of trans-1,4-hexadiene. Combination of Pd3Bi and RhSb gave trans-stilbene in the hydrogenation of diphenylacetylene through partial hydrogenation into cis-stilbene on Pd3Bi and subsequent isomerization on RhSb. RhPb2 exhibited higher activity and selectivity than Rh for the chemoselective hydrogenation of p-nitrostyrene into p-aminostyrene. The higher selectivity of intermetallic compounds than monometals is discussed based on their unique atom arrangement on the surface of intermetallic compounds originating from their regular crystal structures.
Recent focus on ocean plastics pollution, and the decision to ban waste plastic import by China have significantly impacted several industrial sectors around the world. Yet, the global waste plastic generation is steadily growing, which has driven substantial and rapid growth in worlds’ plastics recycling capacity to meet the needs for sustainable plastics use. In Japan, the Resource Circulation Strategy for Plastics was formulated in May 2019. One of the highlights of this Strategy was the milestones established: 25 % reduction of single-use plastics by 2030, 60 % reuse/recycling of plastic containers and packaging by 2030, complete waste plastic utilization through reuse and recycling by 2035, and introduction of ∼2 Mt of bio-based plastics by 2030. Thus, immediate and substantial promotion of research and development of technologies for plastic waste recycling and creation of social and legislative frameworks for accelerating plastic recycling are in high demand. To enable substantial enhancement in the world’s recycling capacity, we believe that feedstock recycling via pyrolysis technologies is of considerable importance. Thus, this review firstly summarizes global trends in waste plastics recycling and examines the trends and challenges regarding pyrolysis technologies, such as reactor design and effective catalytic pyrolysis, toward chemical feedstock recovery from polyolefinic plastics. The authors’ current project on feedstock recycling, i.e., development of pyrolysis technologies using existing petroleum refinery processes, is introduced, and the potential sources of waste polyolefinic plastics, based on material flow analysis, are discussed.
Local structures of Ni species were studied in the NiO/γ-Al2O3 catalyst prepared by the impregnation method for the decomposition of dimethyl sulfide (DMS). Calcination and sulfurization conditions of the prepared catalyst affected the catalytic activity for DMS decomposition. The decomposition performance was increased with sulfurization by H2S compared to sulfurization with DMS prior to the reaction test. X-ray diffraction and X-ray photoelectron spectroscopy analyses indicated that the active sites are NiS. Furthermore, in-situ X-ray absorption spectroscopy analysis was conducted to investigate the fine structural changes of Ni species before and after the sulfurization treatment. For the catalyst calcined at 500 °C, Ni species were present as NiO and NiAl2O4 at a ratio of ca. 4 : 6 and only NiO was sulfurized to NiS which acts as the active sites. In contrast, for the catalyst calcined at 800 °C, Ni species were almost completely present as the Ni component in the NiAl2O4 structure, which is less susceptible to sulfurization than NiO. Therefore, the NiS amount in the catalyst calcined at 800 °C was significantly reduced, leading to lower decomposition activity.
Recently, microwave-assisted demulsification has been proposed using characteristics of both the selective heating of water phase and the local heating at interface in processes of petroleum production and refining. However, the mechanism has not been understood perfectly. In this study, interfacial tension of oil-water system was measured during and after microwave irradiation at the different condition of surfactant concentration. According to the profiles of interfacial tension, it was found that the quick increase was observed due to the energy concentration by microwave absorption at the interface. The level of interfacial modification was discussed through our dimensionless number about the energy concentration, ant the reason is that surfactant desorption was caused by rotation of both water molecule and polar substituent of surfactant. In the future, microwaves can be expected as a new demulsification method.
In general, ZnO is difficult to reduce due to the strong oxygen affinity of Zn, preventing the formation of pure intermetallic NiZn phase under mild conditions. The present study found that CaH2 reducing agent allowed the low temperature synthesis of single phase intermetallic NiZn bulk nanopowder (BET surface area = 6.6 m2/g, crystallite size = 26.9 nm) from a precursor of Ni, ZnO, and Ni3ZnC in molten LiCl–KCl at temperatures as low as 360 °C. Single phase NiZn was obtained in the inert gas flow condition, so CaH2 in molten salts was considered to act as a superior reducing agent to prepare pure intermetallic nanopowders. SEM revealed that the obtained powder consisted of spherical particles of nanometer sizes and small particles were interconnected to form a porous structure. SEM-EDX and XPS of the residues on the samples confirmed that any impurity species originating from LiCl, KCl and CaH2 were efficiently washed out by post-rinsing treatments.
Combinations of Cu-based catalysts and acidic zeolite were investigated for dimethyl ether (DME) production from a mixture of CO2 and H2. The physical mixture of Cu/a-ZrO2 (a-: amorphous) catalyst and protonated FER-type zeolite produced a higher yield of DME than that of a Cu/ZnO/Al2O3 catalyst and FER-type zeolite at high pressure of 1.0 MPa. Cu/a-ZrO2 catalyst showed relatively low activity in terms of undesirable CO formation, and the FER-type zeolite combined with the Cu/a-ZrO2 catalyst had good activity for methanol dehydration, leading to the high yield of DME. DME selectivity over the combination catalyst of Cu/a-ZrO2 and FER reached almost 40 %.