Masa-aki Ohshima

Preliminary study on mechanism of naphthalene hydrogenation to form decalins via tetralin over Pt/TiO2

Abstract To clarify the mechanism of naphthalene hydrogenation to cis - and trans -decahydronaphthalene (decalins) via tetrahydronaphthalene (tetralin), the rate of naphthalene hydrogenation was compared with those of tetralin and tetralin containing 3–10 mol% naphthalene over a TiO 2 -supported Pt catalyst. Tetralin was hydrogenated to decalins readily, while the naphthalene hydrogenation did not take place under the same reaction conditions (433 K and 2.96 MPa). When 3–10 mol% naphthalene was added to tetralin, the rate of hydrogenation decreased clearly with an increase of naphthalene content. The observation suggests that naphthalene interacts with surface metals strongly and prevents the hydrogenation of tetralin.

Effect of residual Cl− derived from metal precursors on catalytic activity in the hydrogenation of naphthalene over supported Pd catalysts

Abstract Hydrogenation of naphthalene was performed over supported Pd catalysts prepared from precursors that contained Cl − and from precursors that were free of Cl − . The activity of catalyst prepared from PdCl 2 was much higher than that prepared from Pd(NH 3 ) 2 (NO 2 ) 2 . The species of Pd precursor strongly affected the activity of Pd/Al 2 O 3 , whereas no significant influence was observed in the effect of Pd/SiO 2 , because residual Cl − was easily removed by calcination and/or reduction. Catalytic activity was increased by addition of NH 4 Cl to Cl − -free Pd/Al 2 O 3 . Residual Cl − was concluded to enhance the catalytic activity of the supported Pd catalysts.

Support effect of Pd/AlPO4 catalyst in hydrogen storage of organic hydride method in the presence of CO

In order to examine the capability of AlPO4 to serve as a catalytic support, we analyzed naphthalene hydrogenation over Pd/AlPO4 catalyst in the presence of CO. This process is an effective storage strategy in the organic hydride method that uses low grade hydrogen. Pd/AlPO4 demonstrated high activity in naphthalene hydrogenation similar to Pd/SiO2–Al2O3, and retained the activity in much higher extent in the presence of CO as compared to Pd/Al2O3. The existence of acidic sites on the surface of AlPO4 was confirmed by ammonia adsorption. FT–IR analysis of adsorbed CO after high temperature evacuation revealed that CO desorbed more easily on Pd surface when supported on acidic materials. Detailed analysis of the IR spectra suggested that acidic support decreased the electronic density of Pd and weakened the adsorption bond. Because CO retardation decreased on acidic supports, Pd catalysts demonstrated high activity in the presence of CO. We found that AlPO4 was an effective acidic support for Pd catalyzed hydrogenation.

Cyclodimerization of crotonaldehyde to form cyclohexadienecarbaldehydes and tolaldehydes over solid base catalysts

The cyclodimerization of crotonaldehyde was performed over acid or base catalysts in the gas phase. We first attempted the reaction over various acid and base catalysts using a pulse reactor. The typical bases, CaO and MgO, effectively promoted the reaction to form methylcyclohexadienecarbaldehydes (MCHC) and tolaldehydes. In contrast, no significant formation of the dimers was observed over the acid catalysts, such as SiO2–Al2O3 and H-mordenite. Aluminum oxide also promoted the dimerization, indicating that the dimerization proceeds on the weaker base sites. The main products in the formed dimers were 6-methylcyclohexa-1,3-dienecarbaldehyde and o-tolualdehyde. In addition, small amounts of 4-methylcyclohexa-1,5-dienecarbaldehyde and p-tolaldehyde were produced as dimers. When the dimerization was performed over CaO, MgO, and Al2O3 using a fixed-bed flow reactor, the catalytic activities of all the catalysts significantly decreased during the initial stage of the reaction. The TG–DTA analysis of the used catalysts clearly indicated that a large amount of the condensation products had adsorbed on the catalyst surface. The maximum selectivity to the dimers (MCHC and tolaldehydes) was 38% for an approximate 30% conversion, which was obtained during the initial stage of the reaction over the Al2O3 and CaO catalysts.