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Ammonia decomposition on Ru/MgO was strongly affected by the pore structure of the MgO support. We found that highly active Ru/MgO catalysts were successfully prepared by using Ru hydroxide and hyd...

The reverse water–gas shift reaction (RWGSR) using a supported ionic liquid-phase (SILP) catalyst consisting of Ru catalyst, ionic liquid (1-butyl-3-methylimidazolium chloride ([C4mim]Cl)), and porous silica gel support, was investigated. The catalytic activity of the SILP catalyst toward RWGSR strongly depends on the kind of Ru catalyst and amount of IL. Among the three kinds of Ru catalysts ([RuCl2(CO)3]2, Ru3(CO)12, and RuCl3), [RuCl2(CO)3]2 exhibits the best catalytic activity. Brunauer–Emmett–Teller (BET) surface area analysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses of the SILP catalyst based on [RuCl2(CO)3]2 and [C4mim]Cl revealed that both the solvation of the active catalytic Ru species and the surface area of the ionic liquid phase strongly affect catalytic activity. Hence, these factors help to determine the optimum amount of [C4mim]Cl in the SILP catalyst. The resulting SILP catalyst, with an optimum constitution, exhibited greater catalytic activity than the homogeneous system in which the same amounts of [RuCl2(CO)3]2 and [C4mim]Cl were employed. Catalytically active Ru species during RWGSR in both systems were investigated by means of electrospray ionization-mass spectrometry (ESI-MS). Interestingly, the rate-determining step in the two systems was different, implying that the silica support lowers the activation energy of the protonation reaction in the catalytic cycle. Therefore, the facilitation of the RWGSR by a SILP catalyst system can be realized by good mass transport, derived from the large surface area, as well as the effect of the silica support on activation energy. Furthermore, 20 cycles of the RWGSR using the SILP catalyst were accomplished.

Vapor phase catalytic transfer hydrogenation (CTH) of aqueous levulinic acid (LA) with formic acid as hydrogen source over different copper catalysts is reported. The Cu–SiO2 showed the highest LA conversion (56%) and selectivity to γ-valerolactone (GVL, 87%) at 250 °C. Analysis indicates that the presence of acid sites are responsible for the cleavage of C–O bonds forming angelicalactone intermediate followed by its hydrogenation to GVL over copper species. Even though the acid sites are necessary a quantitative correlation between acid sites and LA conversion was not observed. Characterization indicated that the higher conversion over Cu–SiO2 can be related to metal support interaction as evident from higher reduction temperature of copper species in H2-TPR compared to other catalysts.

In this work, the conversions of ethanol to propylene and ethylene to propylene were investigated over H-ZSM-5 zeolite catalysts with different SiO2/Al2O3 ratios (80 and 280). The effect of operating conditions (contact time and reaction pressure) has been studied. Special attention has been paid to the effect of reaction pressure on the propylene yield, space time yield and catalyst deactivation. Results show that the H-ZSM-5(280) catalyst was more stable for the ethanol or ethylene conversion reaction. High operating pressure favors the propylene production. However, the higher pressure leads to faster coking.

Dry reforming of methane at 400–600°C was studied over Rh catalysts with different supports (SiO2, γ-Al2O3, α-Al2O3, TiO2, ZrO2, CeO2, Y2O3, SiO2-Al2O3, SiO2-MgO, SiO2-TiO2), Rh particle sizes (1.5–15.6 nm), and acidic properties (acidic site density, 0.37–3.40 mmol g−1). Catalysts with a high density of strongly acidic sites (e.g., α-Al2O3, SiO2-MgO) showed low activity and gradually deactivated with time on stream; in contrast, catalysts with a low density of strongly acidic sites (e.g., TiO2, γ-Al2O3) showed high, stable activity. Rh/SiO2-TiO2 showed the best performance, with H2 and CO yields of 1.8% and 4.2% at 400°C and yields 37.3% and 53.1% at 600°C, respectively. Catalyst activity depended strongly on Rh particle size; specific activity increased with decreasing particle size, indicating that Rh-catalyzed dry reforming of methane is structure-sensitive. The support type influenced not only the dispersion and reducibility of the Rh particles but also the specific activity of the catalysts. CO temperature-programmed desorption and FT-IR suggested that electron-deficient Rhδ+ species were generated by electronic interactions between the Rh particles and the support, and the number of these species strongly influenced the overall catalytic activity.

The yttrium-modified zirconia catalysts were prepared by co-precipitation method. N 2 adsorption/desorption method, temperature programmed desorption and X-ray diffraction were used to characterize the Y/ZrO 2 catalyst. All the catalysts were tested in the conversion of ethanol to propylene. The propylene yields showed a volcano-shaped dependence on the Y amount. The maximum yield of propylene reached 44.0%. The results implied that Y/ZrO 2 catalyst with tetragonal structure or bigger specific BET surface area showed better performance. Reaction pathways were suggested to be ethanol to ethylene on the acidic sites, and ethanol → acetaldehyde → acetone → propylene on the basic sites.

Vapor phase catalytic transfer hydrogenation of aqueous levulinic acid (LA) with formic acid (FA) as a hydrogen source was carried out over copper loaded on to several SiO2 supports having different physicochemical properties. The SiO2 supports and Cu–SiO2 catalysts with different support properties were characterized by XRD, TPR, XPS, NH3-TPD and UV-vis techniques to evaluate the copper species and its interaction with the support. The SiO2 support alone showed lower LA conversion and low selectivity to GVL whereas Cu–SiO2 catalysts were found to show high conversion and selectivity to the desired product with formic acid as the hydrogen source. The difference in the activities and product selectivity among different copper supported silica appears to be a complex function of acidity and the nature of copper species in the Cu–SiO2 catalysts. No direct correlation was observed between a specific catalyst property such as acidity and pore size, and the performance of the Cu–SiO2 catalysts. From the characterization, it appears that the species responsible for higher activity and selectivity to GVL are monomeric partially oxidized copper species in a strong interaction with the support in combination with a higher number of acid sites, both of which are present in Cu–SiO2-Q6. Cu–SiO2-Q6 showed the highest conversion and selectivity of 66 and 81%, respectively, under optimized conditions.

The decomposition of NH 3 over Ni catalysts supported on various metal oxides (Y 2 O 3 , CeO 2 , MgO, La 2 O 3 , Al 2 O 3 , and ZrO 2 ) was investigated, and the Ni/Y 2 O 3 catalyst was found to show the highest activity. The rate of H 2 formation per exposed Ni atom (turnover frequency) for the supported Ni catalysts depended strongly on the type of metal oxide support, indicating that the active sites for the Ni catalysts were not identical in nature. Investigation of the associative desorption of atomic nitrogen formed by NH 3 decomposition over the Ni catalysts revealed that the N 2 desorption temperature depended on the type of support. This result indicates that the Ni N binding energy varied among the metal oxide supports, which would be attributable to the change of the Ni electronic state by the supports. The volcano-curve relationship was obtained between turnover frequency and N 2 desorption temperature, indicating that the NH 3 decomposition activity was dominated by the Ni N binding energy. We considered that the metal oxide supports changed the rate-determining step for NH 3 decomposition on Ni.

A layered double hydroxide (LDH) type adsorbent for phosphate removal from aqueous solution was prepared from blast furnace slag (BFS) which is vastly discharged by the iron manufacturing industry....

Side reactions of the ethanol-to-butadiene conversion catalyzed by MgO or ZnO were analyzed by density functional theory. We examined acetaldehyde disproportion to generate ethyl acetate, the hydrolysis of ethyl acetate to acetic acid, and the ketonization of acetic acid to generate acetone and CO2. The reactivities of these reactions on MgO and ZnO were compared. Our results revealed that among the three reactions, the difference in reactivity between the two oxides was greatest for the ketonization reaction—there was a higher activation barrier on MgO than on ZnO. This would cause the higher ratio of by-products on ZnO than on MgO.

In this study, H-ZSM-5 catalysts with different particle sizes were prepared by adding different amount of water to the starting gel before crystallization. These H-ZSM-5 catalysts were characterized by scanning electron microscopy, N2 adsorption/desorption measurements, X-ray fluorescence, X-ray diffraction, and temperature programmed desorption of ammonia. It was found that the olefin (ethylene, propylene and butene) yield decreased with the increase in the particle size of the catalysts. The paraffin (ethane, propane and butane) yield trended to increase with the increase of particle size. The C5 + products yield increased considerably with the increase of particle size. The results implied that the formation of the C5 + products and hydrogen was inhibited over the smaller particle size catalyst, furthermore the formation of paraffin decreased. So the propylene yield could be increased over smaller H-ZSM-5 catalyst.

Professor Masatake Haruta’s distinguished scientific achievements are highlighted in heterogeneous catalysis by gold (Au). In 1982, he discovered that Au became highly active for CO oxidation even at 200 K when gold was deposited as nanoparticles (NPs) smaller than 5 nm on 3d transition metal oxides. After this finding, he and his co-workers have developed many preparation methods for the deposition of Au as NPs and clusters onto a wide variety of supports. By kinetic, theoretical, and surface science studies, Haruta and co-workers revealed interesting catalytic features of Au, including reaction mechanisms which are greatly different from those of Pd and Pt. Haruta and co-workers also found that supported Au NPs catalyzed direct oxidation of propylene to propylene oxide using O2 and H2, and subsequently O2 alone in the presence of H2O.

Kattel et al . (Reports, 24 March 2017, p. 1296) report that a zinc on copper (Zn/Cu) surface undergoes oxidation to zinc oxide/copper (ZnO/Cu) during carbon dioxide (CO 2 ) hydrogenation to methanol and conclude that the Cu-ZnO interface is the active site for methanol synthesis. Similar experiments conducted two decades ago by Fujitani and Nakamura et al . demonstrated that Zn is attached to formate rather than being fully oxidized.

Gold nanoparticles supported on base metal oxides exhibit high catalytic activity in the low temperature oxidation of CO. Numerous studies have been carried out by using powder, single crystal, and planar model catalysts together with density functional theory calculations to elucidate the reaction mechanism and the nature of the active sites. A characteristic feature of these catalysts is that the moisture contained in the catalyst and in the reactant gas markedly enhances CO2 formation rates. The promoting role of moisture, which is advantageous for the practical applications to air purifiers, can be classified into four categories: (i) maintain cationic state of gold (Au3+ or Au+), (ii) direct involvement of H2O and OH− groups in CO oxidation, (iii) activation of O2 molecules, and (iv) transformation of catalytic intermediates and inhibitors (spectators) such as carbonate species. The elucidation of the role of water in CO oxidation will deepen the understanding of the unique catalysis by gold.

Esterification of levulinic acid with ethanol to produce ethyl levulinate was examined by using sulfated Si-doped ZrO 2 solid acid catalysts with enlarged surface areas and the relationships between the structural properties and catalytic performances were investigated. Structures of the catalysts were verified by XRD, nitrogen physisorption, FE-SEM, UV–vis and FTIR measurements. Acidity of the catalysts that substantially affect the catalytic activity was evaluated by NH 3 -TPD measurement. Incorporation of Si atom into the lattice structure of ZrO 2 (up to 30 mol% Si per Zr atom) afforded high-surface-area SiO 2 -ZrO 2 mixed oxides, and their sulfated forms provided increased numbers of sulfate anions and the associated acid sites. Several distinct correlations were found between the structural properties/acidities and catalytic activities, which suggested that (i) the number of accessible active acid sites and (ii) the accessibility of the organic reactants to the active sites play crucial roles in determining the overall activity. Among the catalysts tested, sulfated Si-doped ZrO 2 with optimum Si content (5.0–10 mol% Si per Zr) was found to be the best catalyst, the activity of which was far superior to that of the conventional sulfated ZrO 2 . In addition, direct conversion of cellulosic sugars (glucose and fructose) into levulinate esters was also examined, in view of their practical applications in acid-catalyzed biomass conversion processes.

Production of propylene from ethanol was studied over ZSM-5 co-modified with zirconium and phosphorus (P/Zr/ZSM-5). XRD and NH3-TPD were used to characterize P/Zr/ZSM-5 together with H-ZSM-5 and the zirconium modified ZSM-5 (Zr/ZSM-5) for comparison. It was found that the concentration of strong acid sites on P/Zr/ZSM-5 was significantly reduced by the impregnation of phosphorus into Zr/ZSM-5. In the ethanol-to-propylene reaction, P/Zr/ZSM-5 exhibited a better catalytic performance than H-ZSM-5 and Zr/ZSM-5. The in situ UV–Vis spectrum of the ethanol adsorbed P/Zr/ZSM-5 revealed that the species of non desorbed aromatics were hardly produced and thus the formation of carbonaceous deposits was inhibited by the phosphorus modification.

We investigated the effects of added phosphorus on the conversion of ethanol to propylene over ZSM-5 zeolite catalysts. We found that the activity of the catalysts was enhanced by the addition of phosphorus, and we suggest that the added phosphorus suppressed oligomerization of propylene and butene by decreasing the acidity of the active sites of the zeolites. Furthermore, the addition of phosphorus greatly enhanced the hydrothermal stability of the zeolites and thus substantially improved the catalyst durability during ethanol conversion. Carbon deposition, which was the main cause of deactivation of the phosphorus-modified zeolites, was suppressed by H2O produced by dehydration of ethanol.

Protonated ZSM-5 zeolites (HZSM-5(M), M = Al, Ga, and Fe) having different acid strengths were prepared under various synthesis conditions, and the effect of acidity of the ZSM-5 zeolite on the conversion of ethanol to propylene was investigated in detail. HZSM-5(Ga) and HZSM-5(Al) showed high propylene yields. However, HZSM-5(Fe) yielded ethylene instead of propylene, i.e., only dehydration of ethanol occurred on HZSM-5(Fe). These results indicate that the acid strength is a crucial factor for the selective production of propylene. In other words, for successful selective conversion of ethanol to propylene, HZSM-5(M) zeolites must contain acid sites with an acid strength that is more than that of HZSM-5(Ga). It was also found that phosphorous-modified HZSM-5(Ga) zeolite exhibited an improved propylene yield relative to the unmodified zeolite and that the modification considerably enhanced the catalytic stability because of the suppression of both elimination of framework gallium and coke deposition.

Gold nanoparticles on titanium oxide and titania-silica supports are active for the formation of propylene oxide by the oxidation of propylene with hydrogen and oxygen mixtures. Cyanide treatment of gold supported on titanosilicate zeolite supports (Au/TS-1) yielded unexpected results. Catalysts treated with weak solutions of sodium cyanide resulted in preferential removal of small gold particles, while catalysts treated with strong solutions resulted in dissolution of the gold and re-precipitation as gold (+1) cyanide. X-ray absorption spectroscopy demonstrated that catalysts that produce propylene oxide in the presence of hydrogen and oxygen mixtures had supported gold (+3) oxide nanoparticles of 3 nm size after synthesis, which were reduced to gold metal at reaction conditions. Samples treated with strong solutions of sodium cyanide resulted in supported gold (+1) cyanide particles of large size, 9–11 nm. These particles did not produce propylene oxide but, surprisingly, showed high selectivity toward propylene hydrogenation. Increasing gold (+1) cyanide particle size resulted in a decrease in hydrogenation activity.

The influence of seed crystals on the interzeolite conversion of FAU type zeolite into CHA type zeolite was investigated in the presence of benzyltrimethylammonium hydroxide as a structure-directing agent under various hydrothermal synthesis conditions. Pure and highly crystalline CHA type zeolites with a wide range of Si/Al ratios were obtained in a shorter crystallization time as compared with those obtained without seed crystals. Furthermore, we achieved the first successful synthesis of high-silica CHA type zeolite in the absence of Na + cations by increasing the seed content. The protonated CHA type zeolite with a Si/Al ratio of ca. 15 yielded the highest propylene yield of ca. 48 C-% in ethanol conversion into light olefins.

Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to investigate the coordinative states of surface Al species on various triethylaluminum (TEA)-modified Phillips CrO x /SiO 2 catalysts under different Al/Cr molar ratios. 1 H and 27 Al MAS NMR spectra clearly demonstrated that the existing states of surface Al species in TEA modified catalysts strongly depended on the concentration of TEA and on the calcination temperature used during the catalyst preparation process. 1 H MAS NMR spectra of TEA-modified Phillips CrO x /SiO 2 catalysts calcined at three different temperatures exhibited similar trends in peak shifts with increasing Al/Cr molar ratios, but the sensitivity dependence of variation in chemical shift of the main peaks on Al/Cr molar ratios increases with increasing of calcinations temperature. This increased sensitivity might have been due to the relatively low amount of residual hydroxyl groups present on the silica support after catalyst calcination. 27 Al MAS NMR spectra showed the presence of three different coordination states (6-, 5-, and 4-coordinated Al species) in the TEA-modified Phillips catalysts. At relatively low Al/Cr molar ratios, the 6-coordinated Al species was the dominant species observed in the catalysts. However, the 4-coordinated Al species became dominant at relatively high Al/Cr ratios for TEA-modified catalysts calcined at 600 and 800 °C, because the increase in TEA concentration might have decreased the amount of oxygen atoms surrounding each Al species. After a saturation state of Al species directly coordinated on the catalyst or silica surface reached, residual TEA coordinated with the Al species already coordinated on the catalyst or silica surface, thus increasing the coordination number of the Al species. Consequently, the 6-coordinated Al species became predominant again for the TEA-modified catalysts calcined at 600 and 800 °C.

In this work, phosphorus-modified ZSM-5 zeolites were used to transform ethanol to propylene. The selectivity of propylene formation depended strongly on the phosphorus content in the zeolites; the highest propylene yield (32%) was observed over H-ZSM-5(80) modified with phosphorus at a P/Al molar ratio of 0.5. The enhancement of propylene selectivity with increasing phosphorus content was attributed to reduction of strong acid sites on the H-ZSM-5. Modification of the zeolite with phosphorous also improved the material's catalytic stability.

Industrial demand for propylene is increasing. Alternative sources of propylene other than petroleum are of wide interest. The catalytic transformation of bioethanol is a promising avenue for the production of propylene. However, the reaction mechanism and the nature of active sites on the catalyst remained unclear. In this work, MFI-type zeolite catalysts with various Si/Al2 ratios (73, 97, 128, 176, 207) were prepared by hydrothermal synthesis under atmospheric pressure. We characterized these MFI catalysts by BET surface area measurements, X-ray fluorescence, X-ray diffraction, scanning electron microscopy, temperature programmed desorption of ammonia, and 27Al MAS NMR to understand the effect of the Si/Al2 ratio. The ethanol conversion reaction was systematically investigated using these catalysts according to the contact time and reaction temperature. The conversion of ethanol yielded similar product distributions over these catalysts at different contact times, indicating that the product distribution has no relationship with the Si/Al2 ratio. Also, the propylene production rates per acidic site of these catalysts were similar. These results strongly imply that the acidic sites of the different MFI-type zeolite catalysts have the same nature, as well as the same reactivity. The catalytic activity was proportional to the number of acidic sites.

A series of Au/titanium silicalite-1 (TS-1) catalysts with different Si/Ti ratios and promoted with alkali and alkaline earth cations were prepared by deposition–precipitation (DP) and tested for direct propylene epoxidation. It was found that the gold loading and catalytic activity was highly dependent on the pH of the DP synthesis solution and the final composition of the catalyst. Addition of Group 1 metals such as K or Cs had little effect on the gold content, but increased activity, while Group 2 metals such as Mg, Ca, Sr, and Ba increased both the gold content and the catalytic activity. The highest improvement was provided by a Mg promoted catalyst, which at 443 K and 0.1 MPa with a H 2 /O 2 /C 3 H 6 /Ar = 1/1/1/7 feed mixture gave a propylene oxide (PO) formation rate of 88 gPO h −1 kg cat −1 , compared to 57 gPO h −1 kg cat −1 for an unpromoted catalyst, corresponding to a 50% enhancement of activity. Ammonia temperature-programmed desorption (NH 3 -TPD) measurements indicated little change in adsorption amount with promotion indicating that the yield increase was not due to the elimination of acidic sites on the catalyst. Instead, the improved catalytic performance was ascribed to increased Au capture efficiency and dispersion by the catalyst. The effect of Si/Ti ratio, pH of synthesis, and the promoter ions on the gold content could be understood from their effect on the surface charge of the support.

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.

In this work, we studied the conversion of ethanol to propylene over ZSM-5 zeolites. The catalytic performance of H-ZSM-5 (Si/Al2 = 30, 80, and 280) and ZSM-5 (Si/Al2 = 80) modified with various metals was investigated. H-ZSM-5(Si/Al2 = 80) afforded high propylene yield, which indicates that a moderate surface acidity favored propylene production. Zr-modified ZSM-5(80) gave the highest yield (32%) of propylene at 773 K. Furthermore, the catalytic stability of the zeolite was improved by the modification of zirconium. The surface acidity and the presence of metal ions played important roles on the production of propylene.

The highly crystalline and pure LEV zeolite was obtained from the hydrothermal conversion of FAU zeolite as a crystalline aluminosilicate source in the presence of choline hydroxide. As LEV zeolite was not obtained from a conventional amorphous aluminosilicate gel, the advantage and uniqueness of the hydrothermal conversion of FAU zeolite was proven. The hydrothermal conversion of FAU zeolite into LEV zeolite depended significantly upon the Si/Al ratio of the starting FAU zeolite. Only the FAU zeolites with Si/Al ratios of 16–22 were converted into LEV zeolite. Most of all choline species as a SDA existed intact in zeolitic pores. As expected, the protonated LEV zeolite exhibited a good performance for conversion of ethanol to light olefins. The product yields were 35.8% of C2H4 and 34.4% of C3H6.

Adsorption and reactions of NO over the clean and CO-preadsorbed Ir(111) and Rh(111) surfaces were investigated using infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD). Two NO adsorption states, indicative of hollow and atop sites, were present on Ir(111). Only NO adsorbed on hollow sites dissociated to Na and Oa. The dissociated Na desorbed as N2 by recombination of Na and by a disproportionation reaction between atop-NO and Na. Preadsorbed CO inhibited atop-NO, whereas hollow-NO was not affected. Adsorbed CO reacted with Oa and desorbed as CO2. NO adsorbed on the fcc-hollow, atop, and hcp-hollow sites in that order over Rh(111). The hcp-NO was inhibited by preadsorbed atop-CO, and fcc-NO and atop-NO were inhibited by CO preadsorbed on each type of the sites, indicating that NO and CO competitively adsorbed on Rh(111). From the Rh(111) surface-coadsorbed NO and CO, N2 was produced by fcc-NO dissociation, and CO2 was formed by reaction of adsorbed CO with Oa from dissociated fcc-NO.

The catalytic activity of Rh/CeO 2 –ZrO 2 for NO reduction by C 3 H 6 under stoichiometric conditions was found to depend strongly on the Ce/Zr composition. Rh/CeO 2 –ZrO 2 with a Ce/Zr molar ratio of 50/50 (Rh/CZ-50/50) had the greatest activity; Ce/Zr = 74/26 (Rh/CZ-74/26), the least. The Rh/CZ-50/50 also showed specifically high intrinsic activity expressed in terms of turnover frequency (TOF). Different characterization techniques revealed that the Rh and CeO 2 –ZrO 2 support interaction varied according to Ce/Zr composition, and high TOF on Rh/CZ-50/50 was accounted for by the strong Rh and CeO 2 –ZrO 2 support interaction. Although the Rh/CZ-74/26 catalyst was the least active, it was able to catalyze NO reduction with C 3 H 6 when O 2 was eliminated from the reaction gas. In situ FT-IR spectroscopy suggested that formate species formed and stabilized on the Rh/CZ-74/26 catalyst poison the catalytically active sites for NO reduction with C 3 H 6 .

A highly desirable selective catalytic reduction (SCR) of NO with real life diesel fuel over Pt supported zeolites with different topologies (Pt-ZSM-5, Pt-FER, Pt-MOR and Pt-BEA) is studied under simulated exhaust conditions. The catalysts are characterized by CO chemisorption, NH 3 -TPD and TGA. The NO conversion ability of these catalysts has been correlated with zeolite structure and acidity. Pt-MOR is found to be the most active catalyst, 90% NO conversion at 300 °C, however Pt-FER showed highly desirable low temperature window, 77% NO conversion below 260 °C. Over ZSM-5, BEA and Y with three dimensional pore structures extensive carbonaceous deposits are observed by TGA which are detrimental to NO conversion. On the other hand, FER zeolite having one dimensional pore structure did not allow extensive coke formation resulting in a highly desired low temperature NO conversion. The results suggest that, NO reduction mainly take place near the zeolite pore opening, which is in reasonable agreement considering the long and bulky molecules in diesel fuel.

Propane epoxidation was carried out by sequential propane dehydrogenation–propylene epoxidation steps using a two-catalyst bed and H2 and O2 as the oxidant mixture. The propane dehydrogenation step used a Au/TiO2 catalyst that was active at the low temperature (443 K) used for the propylene epoxidation step; the latter used a Au/TS-1 catalyst. In situ Au L3-edge X-ray absorption near-edge structure and ultraviolet–visible measurements on Au/TiO2 under propane dehydrogenation conditions showed activation of oxygen on gold nanoparticles and evidence for the formation of adsorbed oxygen intermediate species responsible for the production of propylene. Propane epoxidation with H2 and O2 at 443 K and 0.1 MPa with the dual Au/TiO2 and Au/TS-1 catalysts resulted in an overall propane conversion of 2%, propylene selectivity of 57%, and propylene oxide selectivity of 8%, corresponding to a propylene oxide space-time yield of 4 g kg cat −1 h −1 . The catalysts showed little deactivation and maintained their conversion and selectivity levels for the 12 h duration of the measurements.

The gas-phase epoxidation of propylene was studied over MoO x /SiO2 catalysts in a reaction system with a post-catalytic bed volume. In the reaction of a mixture of propylene and propane with oxygen below 578 K, propylene oxide (PO) was mainly formed from the oxidation of propylene. It was found that the oxidation reaction was very sensitive to the temperature of the post-catalytic space more than the temperature of the catalyst bed, strongly indicating that radical reactions occurring in the post-catalytic bed free space were responsible for the PO formation. The addition of NO increased propylene conversions and PO selectivity at low conversions, confirming that radical reactions were involved in the propylene reactions.

A catalyst consisting of gold supported on a Ti-containing silicate mesoporous material (TUD) with 13-nm pores was used for the epoxidation of propylene with mixtures of H 2 and O 2 . The catalyst activity was enhanced by the addition of a Ba promoter. The pH of deposition was important in controlling the gold loading and particle size. A pH of 7 gave a Au loading of 2.7 wt% and an average particle size of 2.0 nm, as determined by transmission electron microscopy, whereas a pH of 9 produced a much lower Au loading of 0.11 wt% and smaller particles of size about 0.9 nm, as estimated by X-ray absorption fine structure measurements. At 423 K and 0.1 MPa total pressure, the catalyst prepared at pH 7 gave a steady-state propylene conversion of 2.1%, a propylene oxide (PO) selectivity of 79%, and a H 2 efficiency of 3.8%, whereas that prepared at pH 9 gave a conversion of 1.4%, a PO selectivity of 99%, and a H 2 efficiency of 17%. The turnover frequency for PO production based on total gold increased on going to the sample prepared at pH 9. Thus, it is concluded that very small Au particles (about 1 nm) are the most active for epoxidation, whereas larger Au particles (about 2 nm) are less active because they promote direct H 2 oxidation to H 2 O. X-ray absorption near-edge spectroscopy results indicated that at reaction conditions, the small particles had partially oxidized gold but the larger particles had metallic gold, suggesting that the smaller particles had high coverage of oxygen or oxygen-derived species.

In order to improve the catalytic performance of supported-Ir catalysts for the selective reduction of NO with CO, the effect of H2 was investigated. While adding H2 showed no or negative effect on NO conversion on Ir/SiO2, Ba/Ir/SiO2 and Ir/WO3/SiO2 catalysts, the activity of Ba-doped Ir/WO3/SiO2 catalyst for NO reduction was significantly increased by H2 addition. The role of H2 was found to stabilize the catalytically active Ir-WOx sites during the reaction.

The adsorption and reactivity of SO 2 on the Ir(1 1 1) and Rh(1 1 1) surfaces were studied by surface science techniques. X-ray photoelectron spectroscopy measurements showed that SO 2 was molecularly adsorbed on both the Ir(1 1 1) surface and the Rh(1 1 1) surface at 200 K. Adsorbed SO 2 on the Ir(1 1 1) surface disproportionated to atomic sulfur and SO 3 at 300 K, whereas adsorbed SO 2 on the Rh(1 1 1) surface dissociated to atomic sulfur and oxygen above 250 K. Only atomic sulfur was present on both surfaces above 500 K, but the formation process and structure of the adsorbed atomic sulfur on Ir(1 1 1) were different from those on Rh(1 1 1). On Ir(1 1 1), atomic sulfur reacted with surface oxygen and was completely removed from the surface, whereas on Rh(1 1 1), sulfur did not react with oxygen.

The role of the Al2O3 support on the activity of supported Ag catalyst towards the selective catalytic reduction (SCR) of NO with decane is elucidated. A series of Ag/Al2O3 catalysts were prepared by impregnation method and characterized by N2 pore size distribution, XRD, UV–Vis, in-situ FT-IR and acidity measurement by NH3 and pyridine adsorption. The catalytic activity differences of Ag/Al2O3 are correlated with different properties of Al2O3 supports and the active Ag species formed. 4wt% Ag supported on sol-gel prepared Al2O3 (Ag/Al2O3 (SG), showed higher NOx conversion (65% at 400 °C), compared with the respective catalysts made from commercial Al2O3 (Ag/Al2O3 (GB), Ag/Al2O3 (ALO), (∼26 and 7% at 400 °C). The higher surface area, acidity and pore size distribution in sol–gel prepared Al2O3 (SG) results in higher NO and hydrocarbon conversion. Based on the UV–vis characterization, the activity of NO reduction is correlated to the presence of Agnδ+ clusters and acidity of Al2O3 support was found to be one of the important parameter in promoting the formation and stabilization of Agnδ+ clusters. Furthermore from pyridine adsorption results, presence of more number of Bronsted acid sites in Ag/Al2O3 (SG) is confirmed, which could also contribute to low temperature hydrocarbon activation and improve NO conversion. In situ FT-IR measurements revealed the higher rate of –CN and –NCO intermediate species formation over 4wt% Ag/Al2O3 (SG). We conclude that the physico–chemical properties of Al2O3 play a crucial role in NOx conversion over Ag/Al2O3 catalysts. Thus, the activity of the Ag/Al2O3 catalyst can be tailored by using a proper type of Al2O3 support.

Reactions between NO and CO on Rh(1 1 1) surfaces were investigated using infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption. NO adsorbed on the fcc, atop, and hcp sites in that order, whereas CO adsorbed initially on the atop sites and then on the hollow (fcc + hcp) sites. The results of experiments with NO exposure on CO-preadsorbed Rh(1 1 1) surfaces indicated that the adsorption of NO on the hcp sites was inhibited by preadsorption of CO on the atop sites, and NO adsorption on the atop and fcc sites was inhibited by CO preadsorbed on each type of site, which indicates that NO and CO competitively adsorbed on Rh(1 1 1). From a Rh(1 1 1) surface with coadsorbed NO and CO, N2 was produced from the dissociation of fcc-NO, and CO2 was formed by the reaction of adsorbed CO with atomic oxygen from dissociated fcc-NO. The CO2 production increased remarkably in the presence of hollow-CO. Coverage of fcc-NO and hollow-CO on Rh(1 1 1) depended on the composition ratio of the NO/CO gas mixture, and a gas mixture with NO/CO ⩽ 1/2 was required for the co-existence of fcc-NO and hollow-CO at 273 K.

The effect of iridium dispersion on the activity of Ir/SiO2 for the selective reduction of NO with CO in the presence of O2 and SO2 has been investigated. The intrinsic activity, expressed in terms of turnover frequency (TOF), increases with decreasing iridium dispersion, indicating that NO reduction with CO over Ir/SiO2 is a structure-sensitive reaction. Characterization of Ir/SiO2 using TPO, XRD and FT-IR spectroscopy following CO adsorption shows that larger iridium crystallites are more difficult to be oxidized and much easier to be reduced under reaction conditions, resulting in the formation of stable iridium metal sites on which NO reduction occurs.

The effect of metal additives on the catalytic performance of Ir/SiO2 catalyst for the selective reduction of NO with CO in the presence of O2 and SO2 was investigated. Among the 19 additives tested here, the addition of barium was the most effective to enhance the activity of Ir/SiO2 at low temperature and low SO2 concentration. Catalyst characterization suggested that barium prevents catalyst deactivation as an oxidation-retardant for the active Ir metal supported on SiO2.

The influence of deposited potassium on the oxidation and NO reactivity of a Co(0 0 0 1) surface was studied using X-ray photoelectron spectroscopy. The formation of surface CoO was observed when the clean Co(0 0 0 1) surface was exposed to O 2 at 500 K. In contrast, the Co atoms on the K-deposited Co(0 0 0 1) surface remained at a lower oxidation state, CoO x (0 x 2 − species formed on the oxidized K/Co(0 0 0 1) surface. This species is considered to be an intermediate in NO decomposition. It was concluded that the role of potassium was (i) to form the NO 2 − intermediate, and (ii) to keep the Co surface partially oxidized (CoO x ) as the active site for the dissociation of the NO 2 − species.

Comprehensive studies combining surface science and real catalyst were performed to get further insight into catalytic active site and reaction mechanism for NO decomposition over supported palladium and cobalt oxide-based catalysts. On palladium single-crystal model catalysts, adsorption, dissociation and desorption behavior of NO was found to be closely related to the surface structures, the stepped surface palladium being active for dissociation of NO. In accordance with this result, the activity of powder Pd/Al2O3 catalysts for NO decomposition was directly related to the number of step sites exposed on the surface, suggesting that the step sites act as the catalytic active site for NO decomposition on Pd/Al2O3. NO decomposition over cobalt oxide was found to be significantly promoted by addition of alkali metals. Surface science study and catalyst characterization led to the same conclusion that the interface between the alkali metal and Co3O4 serves as the catalytic active site. From the results of in situ Fourier transform infrared (FT-IR) spectroscopy and isotopic transient kinetic analysis, a reaction mechanism was proposed in which the reaction is initiated by NO adsorption onto alkali metals to form NO 2 − species and then NO 2 − species react with the adsorbed NO species to form N2 over the interface between the alkali metal and Co3O4.

Direct epoxidation of propylene by oxygen was investigated over Ag-based catalysts containing an added 3d transition-metal species (Mn, Fe, Co, or Ni). The oxidation of propylene occurred at lower temperatures over Ag-based catalysts containing small amounts of added metal species than over a Ag single catalyst. The yield of propylene oxide (PO) depended strongly on the type of metal: the addition of Ni afforded the highest yield of PO at similar values for the conversion of propylene (4–6%). The highest PO selectivity, four times that obtained with the Ag single catalyst, was obtained at 33 mol% Ni. X-ray diffraction analysis and transmission electron microscopy results showed that the dispersion of Ag particles in the Ag–Ni catalysts increased with increasing Ni content, which suggests that Ni atoms controlled the Ag particle size by suppressing the sintering of Ag particles. The turnover frequency for propylene epoxidation was highest at a Ag particle size of approximately 80 nm.

The effect of coexisting SO 2 on the activity of silica-supported noble metal catalysts for the selective reduction of NO with CO in the presence of O 2 was investigated. Pt/SiO 2 , Rh/SiO 2 , and Pd/SiO 2 showed little catalytic activity for NO reduction, irrespective of coexisting SO 2 . Although Ir/SiO 2 showed no NO reduction activity in the absence of SO 2 , the presence of SO 2 drastically promoted NO reduction. A comparison of the catalytic performance of Ir/SiO 2 and Ir/Al 2 O 3 in the presence of SO 2 showed that Ir supported on SiO 2 is more active than Ir on Al 2 O 3 . SiO 2 was found to be a more effective support than Al 2 O 3 . The most outstanding feature of the reaction on the Ir/SiO 2 catalyst was that the coexistence of SO 2 and O 2 is essential for NO reduction to occur. The role of coexisting SO 2 was considered to be not only to stabilize but also to create Ir 0 sites in an oxidizing atmosphere. FT-IR measurements suggested that a cis-type coordinated species of NO and CO on one iridium atom (Ir NO CO ) was an intermediate for NO reduction by CO. Although the Ir NO CO species completely disappeared with the addition of O 2 to the reaction gas, the presence of coexisting SO 2 caused a reappearance of the Ir NO CO species. A reaction mechanism in which N 2 and N 2 O are produced via the recombination of dissociated N atoms (N (a) + N (a) → N 2 ) and the formation of dimer (NO) 2 -type species (2NO → (NO) 2(a) → N 2 O + O (a) ), respectively, is proposed.

The active sites for direct decomposition of NO on supported palladium catalysts were investigated by a comparative study with single-crystal palladium surfaces. In the study of powder catalysts, the activity of Pd/Al 2 O 3 was found to be significantly affected by the type of palladium precursor. Pd/Al 2 O 3 catalysts prepared from palladium nitrate showed the highest activity, expressed in terms of turnover frequency (TOF), for NO decomposition to N 2 . In studies using single-crystal model catalysts reported previously [I. Nakamura, T. Fujitani, and H. Hamada, Surf. Sci. 514 (2002) 409], the adsorption, dissociation, and desorption behavior of NO was closely related to the surface structures, the stepped surface palladium being active for dissociation of NO. NO adsorption by FT-IR spectroscopy confirmed the presence of the stepped palladium sites on Pd/Al 2 O 3 catalysts, and the specific activity (TOF step ) for NO decomposition to N 2 , calculated on the basis of number of step sites estimated from the amount of chemisorbed NO, was not changed for all the Pd/Al 2 O 3 catalysts. These results suggest that direct decomposition of NO mainly proceeds on the step sites of palladium. This is in agreement with the results obtained for single-crystal model catalysts. The present study shows that the activity of powder catalyst can be well interpreted by its surface structure, indicating the usefulness of surface science techniques.

The influence of Mn deposited on a Pd(100) surface on the adsorption, dissociation and desorption properties of NO has been studied using infrared reflection absorption spectroscopy (IRAS), temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). On the Mn/Pd(100) surface, only the NO adsorbed on the Pd was observed at 320 K. Thermal dissociation of NO did not occur on the clean Pd(100) surface; it did occur, however, on the Mn/Pd(100) surface at 320 K. A Pd-Mn alloy was formed by deposition of Mn onto the Pd(100) surface; the formation of the Pd-Mn alloy was correlated with the activity of NO dissociation, assuming that it was the active site for this dissociation. The oxygen produced from the dissociation of NO was found to destroy the Pd-Mn alloy, forming MnOx. No desorption of oxygen from MnOx on Pd(100) was observed below 1200 K.

The problem concerning the active site and the role of ZnO in Cu/ZnO-based methanol synthesis catalysts can be consistently explained based on the literature results by distinguishing CO2 and CO hydrogenations. Although only metallic copper has some activities for methanol synthesis by the hydrogenation of CO2, Cu-Zn alloying in Cu particles is responsible for the major promotional role of ZnO in industrial Cu/ZnO-based catalysts. The morphology effect reported in the literature will probably appear for the system of highly dispersed Cu particles supported on ZnO. As for the hydrogenation of CO, Cu+ species or Cu-O-Zn sites are the active sites for methanol synthesis. The spillover effect of the Cu-ZnO system is not significant compared to the effect of ZnO on the creation of the Cu-O-Zn site.