The active site and the role of ZnO in Cu/ZnO-based catalysts for methanol synthesis from CO2 and H2 were investigated using both classical catalytic and surface science techniques. The active site model in which Zn species present on the Cu surface promotes methanol synthesis is proposed based on the findings for the powder catalysts such as a physical mixture of Cu/SiO2 and ZnO/SiO2. Zn promotion was confirmed with a model catalyst of a Zn-deposited Cu(111) surface. The mechanism and kinetics of methanol synthesis over Zn/Cu(111) as well as the structure of the active site were studied. Metallic Cu–Zn surface alloy acts a catalytically active species for the methanol synthesis from CO2 and H2. Furthermore, we describe the improvement of catalyst performance and development of catalytic processes based on these findings.
The development of next-generation heterogeneous catalysts for the chemoselective hydrogenation of unsaturated aldehydes to unsaturated alcohols requires extensive structural understanding of active catalyst sites. In the case of SnPt catalysts, the presence of metallic Sn and the formation of Sn–Pt alloys are believed to be key factors strongly affecting the selectivity of unsaturated alcohol formation. This review describes the relationship between the catalytic crotonaldehyde (CH3–CH=CH–CHO) hydrogenation performance of supported and non-supported SnPt catalysts and the structure of the component SnxPty alloys, which reveal that at the same Sn/Pt atomic ratio, the composition of the produced SnxPty alloys depends on the preparation method. The Sn1Pt3, Sn1Pt1, and Sn2Pt1 phases identified in SnPt catalysts exhibited higher crotyl alcohol (CH3–CH=CH–CH2OH) formation selectivity than the monometallic Pt phase. Furthermore, the Sn1Pt1 and Sn2Pt1 phases showed lower crotonaldehyde conversion than the Pt phase. Formation of Sn oxides over the supported SnPt catalysts was confirmed with excess amount of Sn. The crotyl alcohol selectivity increased with the transition from Sn1Pt3 to Sn1Pt1, then decrease with the further transition to the more Sn-rich Sn2Pt1 phase. Thus, the Sn1Pt1 alloy phase was concluded to be the most effective bimetallic SnPt structure for the selective formation of crotyl alcohol.
Gasification technology converts a solid fuel to syngas, and it has wide utility for power generation and hydrogen production. In a dual fluidized bed gasifier, the fuel is gasified with steam. As the gasifier operates at 1073-1173 K, tar is generated in the syngas, and a tar reformer such as a catalytic reforming tower is normally required. To ensure optimal reformer design, it is important to clarify the components of the tar. In this study, the components of tar were investigated using a laboratory-scale fluidized bed gasifier to gasify lignite at 1123 K, employing wide variations in the amount of supplied steam. As the steam supply increased, the tar concentration decreased. In addition, a prediction method in real time of the tar concentration in the syngas which is varied by the amount of steam supplied to the gasifier from the analysis of the hydrogen and carbon monoxide produced was proposed. The tar components were analyzed using various hyphenated techniques such as gas chromatograph mass spectrometry (GC/MS) and field desorption mass spectrometry (FD-MS). The main components detected were polycyclic aromatic hydrocarbons (PAHs) without any substituent groups. It was shown that even if the steam was supplied at triple the required stoichiometric ratio, the tar composition was unchanged.
We studied the synthesis of 1,3-butadiene via the dehydration of crotyl alcohol (2-buten-1-ol) over solid acids. Crotyl alcohol conversion and butadiene selectivity were both 95 % or more over commercial silica–alumina catalysts. However, a sudden decrease in catalytic activity was observed during the reaction. On the basis of the fact that the deactivated catalyst was regenerated by drying at 150-200 °C, it was revealed that the main cause of the catalyst deactivation was the adsorption of water formed during the reaction and not the coke formation. An analysis of the deactivated catalyst indicated that, since the formation of Al–OH by the hydrolysis of the Al–O–Al bond increased the hydrophilicity of the catalyst surface, the adsorption of water on the catalyst surface was promoted, whereas that of crotyl alcohol was probably inhibited. Moreover, on the basis of the catalyst characterization, it was concluded that silica–alumina catalysts with few silanol groups, few alumina-rich zones, and a low Si/Al ratio were preferable.
Recently, high-temperature and high-pressure water technology (“hydrothermal decomposition”) has been applied to various fields, suggesting the potential for recovery technology for aged bitumen. This study investigated the recovering effect of sub-critical water on aged bitumen based on evaluation of the physical properties, chemical properties, and dynamic rheology. Asphalt reacted for 15 min at 350 to 360 °C showed a significant recovering and modifying effects on physical properties such as penetration, softening point and ductility. Similar effects were found in bitumen with different composition. In addition, the chemical properties confirmed that bitumen recovered by the hydrothermal decomposition method has lower molecular weight and reduced oxidation. Bitumen after hydrothermal decomposition had improved fatigue crack resistance and flow resistance compared to virgin asphalt, indicating the potential of hydrothermal decomposition for recycling asphalt mixtures.
Effect of sulfur poisoning on Pt/α-Al2O3 catalysts in steam methane reforming (SMR) was investigated using dimethyl sulfide (DMS). SMR with and without 10 ppm DMS addition was performed over 0.1-2.0 wt% Pt/α-Al2O3 catalysts. Catalyst deterioration occurred at an early stage, but not inactivation in the presence of DMS. Moreover, after the supply of DMS was stopped, the activity was completely restored. DMS in the reaction gas also caused severe sintering of the Pt particles and promoted carbon formation on the 1.0-2.0 wt% Pt catalysts. On the other hand, carbon formation did not occur on the 0.1 wt% Pt catalysts. The Pt sintering and carbon formation behaviors were independent of the SMR activity. These results suggest that three different active sites are formed on the Pt/α-Al2O3. The first is a SMR active site not affected by DMS. The second is an active site that loses activity due to DMS, but completely regenerates after the supply of DMS is stopped. The third is not an active site of SMR but where sintered Pt accelerates methane decomposition to produce carbon.
Regioselective hydrogenation of trans-1-phenyl-1,3-butadiene was studied using modified Pd/MOF catalysts in the liquid phase at 65 °C and PH2 5.0 MPa-G. Metal-organic framework compound, MOF–Cr with MIL-101 structure, was prepared with Cr3+ as the corner cation and terephthalic acid as the linker. NO2–MOF–Cr of the same fundamental structure as MOF–Cr was prepared with nitroterephthalic acid as the linker. Core-shell type MOF was prepared using NO2–MOF–Cr as the core MOF and this was covered with shell MOF–Cr. Amino group obtained by reduction of the nitro group of nitroterephthalic acid in the core MOF was essential to accommodate Pd. Pd was supported only on the core MOF by ion-exchange. Of the two aliphatic C=C double bonds of the substrate, the inner C=C double bond was preferentially hydrogenated on Pd catalyst supported on MOF–Cr and core-shell MOF–Cr. However, the end C=C double bond was preferentially hydrogenated on Pd supported on t-butoxycarbonyl (t-Boc) modified core-shell type MOF due to the steric effect.
Pyridinium and imidazolium ionic liquids with different anions were synthesized and used to extract lignin from red pine. Based on the catalytic depolymerization activity and the recovery of lignin in different ionic liquids, N-allyl-pyridinium chloride ([Apy]Cl) was chosen to extract lignin from red pine. Cellulose was recovered from the [Apy]Cl-solution with methanol, and lignin was recovered with water and acetonitrile, and the maximum recovery of lignin from red pine was 98.7 wt%.