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The oxygen adsorption and its catalytic reaction with hydrogen on Pt–Rh single crystals were studied at the nanoscale by Field Emission Microscopy (FEM) and Field Ion Microscopy (FIM) techniques at 700 K. Both FEM and FIM use samples prepared as sharp tips, apexes of which mimic a single nanoparticle of catalyst considering their similar size and morphology. Oxygen adsorption on Pt-17.4 at.%Rh samples leads to the formation of subsurface oxygen, which is manifested in the field emission (FE) patterns: for O2 exposure of ~3 Langmuir (L), {113} planes appear bright in the emission pattern, while for higher oxygen doses, i.e. 84 L, the bright regions correspond to the high index planes between the {012} and {011} planes. Formation of subsurface oxygen is probably accompanied by a surface reconstruction of the nanocrystal. The subsurface oxygen can be effectively reacted off by subsequent exposure of the sample to hydrogen gas at 700 K. The hydrogenation reaction was observed as a sudden, eruptive change of the brightness seen on the FE pattern. This reaction resulted in the recovery of the initial field emission pattern characteristic of a clean tip, with {012} facets being the most visible. It was shown that the oxygen accumulation-reduction process is completely reversible. The obtained results indicate that the presence of subsurface species must be considered in the description of reactive processes on Pt–Rh catalysts. [ABSTRACT FROM AUTHOR]

Platinum (Pt), palladium (Pd/PdO), and rhodium (Rh) decorated carbon nanotube (CNT) based catalysts were prepared, characterized and their activity was tested in ammonia (NH) and ethanol (EtOH) assisted selective catalytic reduction (SCR) of nitric oxide (NO) at low temperatures (30-300 °C). In addition, the influence of sulphur on NH-SCR activity was investigated. The catalysts were characterized by transmission and scanning electron microscopy, energy-dispersive X-ray analysis, and X-ray diffraction techniques. In addition, IR measurements were done to determine the adsorbed species on the catalyst surface. The maximum NO conversions over the catalysts were as high as 85 % for Pt/CNT (at 192 °C), 54 % for Pd/PdO/CNT (at 291 °C), and 48 % for Rh/CNT (at 292 °C) with NH as the reducing agent. The SO deactivation was the most severe in the case of Pd/PdO/CNTs. In the EtOH assisted SCR the maximum NO conversions were 100 % for Pt/CNT, 98 % for Pd/PdO/CNT and 85 % for Rh/CNT. [ABSTRACT FROM AUTHOR]

The overall NSR operation was tested over a bimetallic Pt/Rh-BaO lean NO trap (LNT) catalyst in the range of 473-673 K with simulated diesel exhausts and compared to monometallic 1 wt% Pt/BaO/γ-AlO and 0.5 wt% Rh/BaO/γ-AlO samples. The results showed the beneficial effect of the simultaneous presence of 0.5 wt% Pt and 0.25 wt% Rh on the catalytic performance under lean-burn conditions at low temperatures. It was observed that both Pt/BaO/γ-AlO and Rh/BaO/γ-AlO, which both were mildly aged, have limited NO reduction capacity at 473 K. However, combining Pt and Rh in the NO storage catalyst assisted the NO reduction process to occur at lower temperatures (473 K). One possible reason could be that the combined Pt and Rh sample was more resistant to aging. In addition, the NO-TPD data showed that the presence of Rh into the Pt/BaO/γ-AlO system has a considerable effect on the spill-over process of NO, accelerating the release of NO at lower temperatures. These results were in a good agreement with the observed higher rate of oxygen release of the bimetallic Pt/Rh catalyst, leaving a significant number of noble metal sites available for adsorption at lower temperatures than that of the monometallic Pt sample. The superior NSR performance of the bimetallic Pt/Rh/BaO/γ-AlO catalyst under lean-burn conditions suggested the existence of synergetic promotion effect between the Pt and Rh components, increasing the NO reduction efficiency in comparison with that of the monometallic Pt and Rh-BaO LNT catalysts. [ABSTRACT FROM AUTHOR]

The activity of Rh/CeO2 for NO reduction by C3H6 was gradually deceased by mixing with ZrO2 until 68 mol%. Rh supported on CeO2–ZrO2 with higher OSC was found to show lower catalytic activity. High OSC of CeO2–ZrO2 would probably stabilize the surface of Rh in oxidized state, resulting in low activity and low efficiency of C3H6 utilization for NO reduction. In situ FT-IR spectroscopy suggested that mononitrosyl species such as Rh(NO)δ− and Rh(NO)δ+ are reaction intermediates in the NO–C3H6–O2 reaction over Rh/CeO2–ZrO2 catalysts. [ABSTRACT FROM AUTHOR]

The catalytic activity of M/Al2O3 catalysts for the reaction of steam reforming of ethanol has been investigated in the temperature range of 300–450 °C. It has been found that the catalytic performance varies in the order of Pt > Pd > Rh > Ru, with Pt exhibiting high activity and selectivity toward hydrogen production, as well as long term stability at low temperatures. It is shown that the reaction occurs in a bifunctional manner, with the participation of both the dispersed metallic phase and the support. Ethanol interacts strongly with the Al2O3 carrier, promoting mainly ethanol dehydration, while in the presence of Pt, catalytic activity is shifted toward lower temperatures. Ethanol decomposition and dehydrogenation reactions dominate at low temperatures, while reforming, water-gas shift and methanation contribute significantly to product distribution. [ABSTRACT FROM AUTHOR]

A series of Rh catalysts on various supports (Al2O3, MgAl2O4, ZrO2, and ZrO2–CeO2) have been applied to H2 production from the ethanol steam reforming reaction. In terms of ethanol conversion at low temperatures (below 450 °C) with 1wt% Rh catalysts, the activity decreases in the order: Rh/ZrO2–CeO2 > Rh/Al2O3 > Rh/MgAl2O4 > Rh/ZrO2. Support plays a very important role on product selectivity at low temperatures (below 450 °C). Acidic or basic supports favor ethanol dehydration, while ethanol dehydrogenation is favored over neutral supports at low temperatures. The Rh/ZrO2–CeO2 catalyst exhibits the highest CO2 selectivity up to 550 °C, which is due to the highest water gas shift (WGS) activity at low temperatures. Among the catalysts evaluated in this study, the 2wt% Rh/ZrO2–CeO2 catalyst exhibited the highest H2 yield at 450 °C, which is possibly due to the high oxygen storage capacity of ZrO2–CeO2 resulting in efficient transfer of mobile oxygen species from the H2O molecule to the reaction intermediate. [ABSTRACT FROM AUTHOR]

Rh was deposited on to a well-characterized 3.1% Pt/SiO2 (InCat-1) parent catalyst by underpotential deposition method to obtain a model Rh–Pt bimetallic catalyst. TEM and EDS was used to determine its mean particle size and bulk composition: the particles of ca. 3 nm contained ca. 60% Pt and 40% Rh. The Rh–Pt catalyst was tested in methylcyclopentane (MCP) reaction between 513 K and 603 K and 60–480 Torr H2 pressure (with 10 Torr MCP). The parent Pt/SiO2 as well as a 5% Rh/SiO2 catalyst were also studied for comparison. Four subsequent treatments with O2 and H2 up to T = 673 K were applied on the bimetallic catalyst before the catalytic runs. The overall activity showed positive hydrogen order on all samples, bimetallic Rh–Pt resulting in the lowest TOF values. Ring opening and hydrogenolysis products, as well as unsaturated hydrocarbons were formed from MCP. The selectivity of ring opening products and fragments over Rh–Pt catalyst was between the values observed on Pt and Rh, while the selectivity towards benzene formation was highest on the bimetallic sample, especially at higher temperatures. “Selective” ring opening occurred on all samples, resulting mostly in 2 and 3-methylpentane and less hexane. Different pretreatments with H2 and O2 affected slightly the dispersion values and the catalytic behavior of Rh–Pt sample. The selectivities of the Rh–Pt catalyst being between the values observed for Pt/SiO2 and Rh/SiO2 indicates that the sample studied represented a real bimetallic catalyst, resembling both components and exhibiting at the same time, new properties in addition to those, characteristic of Pt or Rh. [ABSTRACT FROM AUTHOR]

Metal supported oxide nanostructures are discussed within the framework of the “inverse model catalyst” concept. We show that oxide nanostructures on metal surfaces may be regarded as artificial oxide materials, which display novel properties as compared to bulk oxide compounds and are stabilised by interfacial interactions and two-dimensional confinement effects. This is illustrated for prototypical examples of vanadium oxide overlayers on Rh(111) and Pd(111) surfaces. Structure and morphological changes of the oxide phase on V-oxide/Rh and V-oxide/Pd inverse catalyst surfaces are discussed, and the mass transport problem in catalyst systems during oxidation-reduction cycles is addressed. We demonstrate that the diffusion of oxide cluster over the metal surface provides a effective means of mass transport. The role of metal-oxide interface in determining the oxide nanolayer structure on particular substrate surfaces is investigated, and interfacial chemistry and interfacial strain effects are identified as important parameters. [ABSTRACT FROM AUTHOR]

Rh was deposited on to a well-characterized 3.1% Pt/SiO2 (InCat-1) parent catalyst by underpotential deposition method to obtain a model Rh–Pt bimetallic catalyst. TEM and EDS was used to determine its mean particle size and bulk composition: the particles of ca. 3 nm contained ca. 60% Pt and 40% Rh. The Rh–Pt catalyst was tested in methylcyclopentane (MCP) reaction between 513 K and 603 K and 60–480 Torr H2 pressure (with 10 Torr MCP). The parent Pt/SiO2 as well as a 5% Rh/SiO2 catalyst were also studied for comparison. Four subsequent treatments with O2 and H2 up to T = 673 K were applied on the bimetallic catalyst before the catalytic runs. The overall activity showed positive hydrogen order on all samples, bimetallic Rh–Pt resulting in the lowest TOF values. Ring opening and hydrogenolysis products, as well as unsaturated hydrocarbons were formed from MCP. The selectivity of ring opening products and fragments over Rh–Pt catalyst was between the values observed on Pt and Rh, while the selectivity towards benzene formation was highest on the bimetallic sample, especially at higher temperatures. “Selective” ring opening occurred on all samples, resulting mostly in 2 and 3-methylpentane and less hexane. Different pretreatments with H2 and O2 affected slightly the dispersion values and the catalytic behavior of Rh–Pt sample. The selectivities of the Rh–Pt catalyst being between the values observed for Pt/SiO2 and Rh/SiO2 indicates that the sample studied represented a real bimetallic catalyst, resembling both components and exhibiting at the same time, new properties in addition to those, characteristic of Pt or Rh. [ABSTRACT FROM AUTHOR]

The novel monolithic-type electrochemical promoted reactor (MEPR), filled with thick Rh and Pt coated films on thin yttria-stabilized zirconia (YSZ) plates, has been tested in simulated and real automotive exhaust gas. Ethylene oxidation and NO reduction by C2H4 in presence of oxygen were investigated in laboratory scale while the automotive bench testing was performed in the exhaust of a diesel engine. In all cases electropromotion was achieved, an advance which in addition to their compact and simple design, makes electropromoted units quite promising for automotive exhaust pollution control. [ABSTRACT FROM AUTHOR]