Nobuhiro Iwasa

Steam reforming and dehydrogenation of methanol : Difference in the catalytic functions of copper and group VIII metals

Abstract HCHO species were effectively involved in the steam reforming and the dehydrogenation of methanol over supported copper and Group VIII metal (Ni, Rh, Pd, and Pt) catalysts. It was suggested that the difference in the catalytic performances of copper and Group VIII metals was ascribed to the difference in the reactivity of HCHO species formed in the course of the reactions. On the basis of the mechanisms proposed, novel functions of Pd/ZnO catalysts recently developed were discussed.

Steam reforming of methanol over Pd/ZnO: Effect of the formation of PdZn alloys upon the reaction

Abstract The catalytic performance of Pd/ZnO for steam reforming of methanol (CH 3 OH + H 2 O → CO 2 + 3H 2 ) was greatly improved by previously reducing the catalysts at higher temperatures. The original catalytic functions of metallic palladium were greatly modified as a result of the formation of PdZn alloys. Over the catalysts containing alloys, formaldehyde species formed in the reaction were suggested to be effectively attacked by water, being transformed into carbon dioxide and hydrogen. By contrast, the formaldehyde species decomposed selectively to carbon monoxide and hydrogen over catalysts containing metallic palladium.

New Supported Pd and Pt Alloy Catalysts for Steam Reforming and Dehydrogenation of Methanol

The catalytic performances of supported Group 810 metal (Co, Ni, Ru, Pd, Ir and Pt) catalysts for steam reforming of methanol, CH3OH + H2O → CO2 + 3H2, and dehydrogenation of methanol to methyl formate, 2CH3 OH → HCOOCH3 + 2H2, are markedly affected by the kinds of supports as well as the metals used. The selectivity for steam reforming and the formation of methyl formate was markedly improved when Pd or Pt were supported on ZnO, In2O3 and Ga2O3. The combined results of temperature-programmed reduction, XRD, XPS and AES revealed that Pd-Zn, Pd-In, Pd-Ga, Pt-Zn, Pt-In and Pt-Ga alloys were formed upon reduction. Over the catalysts having an alloy phase, the reactions proceeded selectively, whereas over the catalysts having a metallic phase, methanol was decomposed to carbon monoxide and hydrogen predominantly. It was shown that the reactivity of formaldehyde intermediate over the Pd and Pt alloys was markedly different from that over metallic Pd and Pt. Over Pd and Pt alloys, aldehyde species were stabilized and transformed into carbon dioxide and hydrogen or methyl formate by nucleophilic addition of water or methanol, respectively. By contrast, over metallic Pd and Pt, aldehyde species were rapidly decarbonylated to carbon monoxide and hydrogen.

New catalytic functions of Pd-Zn, Pd-Ga, Pd-In, Pt-Zn, Pt-Ga and Pt-In alloys in the conversions of methanol

Pd and Pt supported on ZnO, Ga2O3 and In2O3 exhibit high catalytic performance for the steam reforming of methanol, CH3OH+H2O→CO2+3HH2, and the dehydrogenation of methanol to HCOOCH3, 2CH3OH→HCOOCH3+2HH2. Combined results with temperature-programmed reduction (TPR) and XRD method revealed that Pd–Zn, Pd–Ga, Pd–In, Pt–Zn, Pt–Ga and Pt–In alloys were produced upon reduction. Over the catalysts having the alloy phase, the reactions proceeded selectively, whereas the catalysts having metallic phase exhibited poor selectivities.

Highly selective supported Pd catalysts for steam reforming of methanol

Steam reforming of methanol, CH3OH + H2O → 3H2 + CO2, was carried out over various Pd catalysts (Pd/SiO2, Pd/Al2O3, Pd/La2O3, Pd/Nb2O5, Pd/Nd2O3, Pd/ZrO2, Pd/ZnO and unsupported Pd). The reaction was greatly affected by the kind of support. The selectivity for the steam reforming was anomalously high over Pd/ZnO catalysts.

Steam Reforming of Methanol Over Pd-Zn Catalysts

Heating the physical mixtures of Pd and Zn selectively yielded PdZn or Pd3.9Zn6.1 alloy. These alloys were highly selective for the steam reforming of methanol.

Steam reforming of methanol over Ni, Co, Pd and Pt supported on ZnO

Pd/ZnO and Pt/ZnO exhibited anomalously high selectivity for the steam reforming of methanol, when PdZn and PtZn alloys phases were developed. The selectivity decreased over the catalysts having metal phases.

Methanol Synthesis from CO2 Under Atmospheric Pressure over Supported Pd Catalysts

Pd/ZnO catalyst exhibits high activity and selectivity for methanol synthesis in the hydrogenation of CO2 under atmospheric pressure. PdZn alloys are formed upon reduction of the Pd/ZnO catalyst at high temperatures. The catalytic activity and selectivity are greatly enhanced upon the formation of such PdZn alloys. The turnover frequency and selectivity of methanol formation are markedly larger than those of a Cu/ZnO type control catalyst.

Difference in the reactivity of acetaldehyde intermediates in the dehydrogenation of ethanol over supported Pd catalysts

Catalytic performances of supported Pd catalysts for the dehydrogenation of ethanol were greatly modified upon the formation of Pd alloy phases. Over Pd–Zn, Pd–Ga and Pd–In alloys, acetaldehyde was selectively produced at lower conversion levels. With the increased conversion level, ethyl acetate was produced at the expense of acetaldehyde. The selectivities for the ethyl acetate formation exceeded that over a Cu/ZnO catalyst. Over metallic Pd, the decomposition of ethanol, C2H5OH → CO + CH4 + H2, occurred to a considerable extent. It was shown that the reactivity of acetaldehyde species over the Pd alloys was markedly different from that over metallic Pd. Over the Pd alloys, acetaldehyde species were stabilized and transformed into ethyl acetate by the nucleophilic addition of ethanol. By contrast, over metallic Pd, aldehyde species were rapidly decarbonylated to methane and carbon monoxide.

Selective hydrogenation of acetonitrile to ethylamine using palladium-based alloy catalysts

Gas phase hydrogenation of acetonitrile has been studied with various Pd-based catalysts using several supports, ZrO2, CeO2, MgO, SiO2, Al2O3, ZnO, Ga2O3 and In2O3. The catalysts may be divided into two groups, one of which includes ZnO, Ga2O3, and In2O3-supported catalysts and another group includes the other catalysts. The catalysts of the former group are less active but selective to the formation of ethylamine (MEA) and diethylamine (DEA). In particular, MEA is preferentially produced with the Pd/ZnO catalyst. These catalytic features may be ascribed to the formation of such Pd alloys as PdZn, Ga5Pd, Ga2Pd5, and In0.52Pd0.48 as confirmed by X-ray diffraction. Compared with these Pd alloy catalysts, the other catalysts including metallic Pd only are more active but less selective to MEA and DEA, similar to Pd black. The activity of Pd alloy catalysts can be improved by preparing the alloys on the surface of CeO2 support while maintaining their higher selectivity to MEA and DEA.