Characterization of the Active Sites on Pt-Loaded ZSM-5 (Pt/ZSM-5) Prepared by an Ion-Exchange Method for the Oxidation of CO at Low Temperatures

Highly dispersed Pt-loaded ZSM-5 (Pt/ZSM-5) catalysts were prepared by a combination of ion-exchange and thermal pretreatment in different temperatures under vacuum. Highly dispersed ion-exchanged Pt²⁺ ions were reduced into Pt⁺ and then Pt⁰, sustaining their high dispersion state with an increase in the thermal pretreatment temperatures up to 773 K. Thus, prepared Pt⁰ highly dispersed in the cavities of ZSM-5 exhibited high catalytic activity for the oxidation of CO with N₂O at 273?K. However, pretreatment at temperatures higher than 973 K led to the aggregation of highly dispersed Pt⁰ clusters, resulting in a decrease in the catalytic activity for low-temperature oxidation.     

Conversion of methane to benzene over Mo2C and Mo2C/ZSM-5 catalysts

The activation and dehydrogenation of CH₂ on Mo₂C and MO₂C/ZSM-5 have been investigated under non-oxidizing conditions. Unsupported Mo₂C exhibited very little activity towards methane decomposition at 973 K. The main reaction pathway was the decomposition of methane to give hydrogen and carbon with a trace amount of ethane. Mixing Mo₂C with ZSM-5 support somewhat enhanced its catalytic activity, but did not change the products of the reaction. A dramatic change in the product formation occurred on partially oxidized Mo2C/ZSM-5 catalyst; besides some hydrocarbons benzene was produced with a selectivity of 70–80% at a conversion of 5–7%. Carburization of highly dispersed MoO₃ on ZSM-5 also led to a very active catalyst: the conversion of methane at the steady state was 5–6% and the selectivity of benzene formation was 85%.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

The effect of sodium on the catalytic activity of ZnO–Al2O3/ZSM-5 and SnO–Al2O3/ZSM-5 for the transesterification of vegetable oil with methanol

In order to elucidate the effect of sodium on the activity of ZSM-5 supported metal oxides catalysts (ZnO–Al₂O₃/ZSM-5 and SnO–Al₂O₃/ZSM-5) for the transesterification of soybean oil with methanol, ZSM-5 supported metal oxides were prepared with and without sodium hydroxide by impregnation. The metal compositions of the ZSM-5 supported metal oxide catalysts and the metal concentrations dissolved from the catalysts to the methylester phase were measured by SEM-EDS and inductive coupled plasma spectroscopy, respectively. The catalytic activity of ZnO–Al₂O₃/ZSM-5 and SnO–Al₂O₃/ZSM-5 containing sodium did not originate from surface metal oxides sites, but from surface sodium sites or dissolved sodium leached from the catalyst surface.     

Characterization and application of a Pt/ZSM-5/SSMF catalyst for hydrocracking of paraffin wax

The microstructured Pt/ZSM-5/SSMF catalysts, for hydrocracking of paraffin wax, have been developed by impregnation method to place Pt onto thin-sheet ZSM-5/SSMF composites obtained by direct growth of ZSM-5 on the sinter-locked stainless steel microfibers (SSMF). The best catalyst is the one with ZSM-5 having a SiO₂/Al₂O₃ weight ratio of 200, delivering ~ 95% conversion with 77.5% selectivity to liquid products or 64.4% selectivity to naphtha at 280 °C. This new approach is capable of increasing the naphtha selectivity with high activity maintenance in comparison with the literature catalysts.     

Promoting Effect of Pt Addition to V2O5/ZrO2 Catalyst on Reduction of NO by C3H6

The effect of Pt addition to a V₂O₅/ZrO₂ catalyst on the reduction of NO by C₃H₆ has been studied by FTIR spectroscopy as well as by analysis of the reaction products. Pt loading promoted the catalytic activity remarkably. FTIR spectra of NO adsorbed on the catalysts doped with Pt show the presence of two different types of Pt sites, Pt oxide and Pt cluster, on the surface. The amount of these sites depends on Pt contents and the catalyst state. Pt atoms highly disperse on the surface as Pt oxide at low Pt content, being aggregated into Pt metal clusters by increasing Pt amount or reducing the catalysts. The spectral behavior of V=O bands on the surface also supports the formation of Pt clusters. It is concluded that Pt promotes the NO–C₃H₆ reaction through a reduction–oxidation cycle between its oxide and cluster form.     

An investigation of the mechanism of the selective catalytic reduction of NO on various metal/ZSM-5 catalysts: reactions of H2/NO mixtures

Several metal/ZSM-5 catalysts (Pt, Rh, Co and Cu/ZSM-5) were studied for the reduction of nitric oxide by a reducing agent which does not contain carbon, such as H₂, in the absence of oxygen. It has been found that these catalysts are very active towards the above reaction with H₂ even at relatively low temperatures, with a reactivity in the order: Pt/ZSM-5>Rh/ZSM 5>Co/ZSM-5>Cu/ZSM-5. Between the above catalysts Co/ZSM-5 was the most selective to nitrogen with a formation of ammonia much lower than that observed on Pt/ZSM-5, Rh/ZSM-5 and Cu/ZSM-5 even at higher hydrogen partial pressures. A comparison between hydrogen, methane and ethane as the reducing agent has been made. In all cases the catalytic activity is higher using hydrogen rather than ethane or methane, the latter being the least active reductant. All data are consistent with a simple redox mechanism of NO reduction, and exclude the participation of carbonaceous deposits or carbon-containing species in the reaction mechanism.     

CO2 and CO adsorption equilibrium on ZSM-5 for different SiO2/Al2O3 ratios

CO₂ and CO adsorption on MFI type zeolites with different SiO₂/Al₂O₃ ratios (ZSM-5(30), ZSM-5(50), ZSM-5(280), and silicalite) were investigated in this study by a static gravimetric analyzer for pure isotherms at 30°C, 65°C, 100°C, and 135°C over the pressure range of 0–10 atm. Adsorption capacity of CO increases with decreasing SiO₂/Al₂O₃ ratios within ZSM-5. The adsorption of CO₂ for decreasing SiO₂/Al₂O₃ ratios, showed stronger adsorption at lower pressures and at higher pressures, the highest capacity varied from ZSM-5(50) to ZSM-5(30). ZSM-5(280) was found to have the highest selectivity for CO₂ within the widest range of pressures and temperatures tested.     

Low-temperature activity for CO oxidation over diesel oxidation catalysts studied by High Throughput Screening and DRIFT spectroscopy

We have investigated the low-temperature activity for CO oxidation for a series of platinum catalysts supported on Al₂O₃, TiO₂, ZSM-5, CeO₂ and ZrO₂-CeO₂. The results show major differences in activity, due to the support for Pt, especially in the presence of water. Improved activity over ceria containing samples in presence of water is likely due to the water-gas shift (WGS) reaction. Studies with in situ IR spectroscopy suggest a surface formate mechanism for the WGS reaction on Pt/CeO₂.     

The promotional effect of Cr on catalytic activity of Pt/ZSM-35 for H2-SCR in excess oxygen

Selective catalytic reduction of NO by hydrogen was studied over Cr modified Pt/ZSM-35 catalysts. The preparation process greatly influenced catalytic activity and sample prepared by co-impregnation method exhibits the best activity. In situ DRIFT studies revealed that on Pt–Cr/ZSM-35, (1) new Pt-NO^δ+ and NO species adsorbed on Pt were detected upon NO + O₂ adsorption; (2) much more ammonia species were formed under reaction condition. Cr addition not only enhanced the adsorption of NO_x but also promoted the formation of surface NH₄⁺ species, which should be the origin of promotional effect of Cr on Pt/ZSM-35 for H₂-SCR reaction.     

The Effect of H2 on Chichibabin Condensation Catalyzed by Pure ZSM-5 and Pt/ZSM-5 for Pyridine and 3-Picoline Synthesis

The effects of H₂ in the feed gasses on the Chichibabin condensation of ammonia with formaldehyde and acetaldehyde for pyridine and 3-picolines synthesis were studied in this work. It was observed that over Pt/ZSM-5 and H-ZSM-5 catalyst hydrogen can moderate the deactivation, depressed the coke formation, slightly lower the initial yield of pyridine bases and increase the selectivity of pyridine over 3-picoline. These effects cannot be simply attributed to the reactant dilution by H₂, while are similar as those of spilt-over hydrogen on a Pt/ZSM-5 catalyst on this reaction. These phenomena are taken as the evidence to support the hypothesis that molecular H₂ is activated by the pure zeolite during the Chichibabin condensation.     

The Role of Support Acidity in the Selective Catalytic Reduction of NO by C3H6 Under Lean-Burn Conditions

Mechanical mixtures consisting of a catalyst (Pt/SiO₂ or Pt/SiO₂–Al₂O₃) and supports of varying acidity (hydrotalcite, SiO₂, SiO₂–Al₂O₃, and ZSM-5 zeolite) were tested for the selective reduction of NO by C₃H₆. A certain degree of support acidity appears to favour N₂ selectivity, but if there are too many acid sites, carbon deposition becomes extensive and leads to catalyst deactivation.     

The Effect of a Changing Lean Gas Composition on the Ability of NO2 Formation and NOx Reduction over Supported Pt Catalysts

Three model catalysts (Pt/Al₂O₃, Pt/TiO₂, Pt/V₂O₅/TiO₂) were examined in regard to their NO₂ formation ability under a changing lean gas composition. The results show that the NO to NO₂ oxidation function as well as the NO _x reduction under lean gas conditions is affected by a change in the lean gas atmosphere. The NO oxidation activity also decreased with time, for Pt/Al₂O₃ and Pt/TiO₂, and a possible explanation may be platinum oxide formation. This deactivation was not observed for Pt/V₂O₅/TiO₂.     

Effect of Si/Al ratio on performance of Pt–Sn-based catalyst supported on ZSM-5 zeolite for n-butane conversion to light olefins

The performance of Pt–Sn-based catalyst, supported on ZSM-5 of different Si/Al ratios were investigated for simultaneous dehydrogenation and cracking of n-butane to produce light olefins. The catalysts were characterized by number of physio-chemical techniques including XRF, TEM, IR spectra, NH₃-TPD and O₂-pulse analysis. Increase in Si/Al ratio of zeolite support ZSM-5 significantly increased light olefin's selectivity, while feed conversion decreases due to lower acidity of support. The results indicated that both the n-butane cracking and dehydrogenation activity to light olefin's over Pt–Sn/ZSM-5 samples with increasing Si/Al ratios greatly enhanced catalytic performance. The catalysts were deactivated with time-on-stream due to the formation of carbon-containing deposits. A coke deposition was significantly related to catalyst activity, while at higher Si/Al ratio catalyst the coke precursors were depressed. These results suggested that the Pt–Sn/ZSM-5 catalyst of Si/Al ratio 300 is superior in achieving high total olefins selectivity (above 90 wt.%). The Pt–Sn/ZSM-5 also demonstrates resistance towards hydrothermal treatment, as analyzed through the three successive reaction-regeneration cycles.     

Aromatization of n-Butane Over Supported Mo2C Catalysts

Similarly to the case of methane, ethane and propane, Mo₂C deposited on ZSM-5 significantly enhanced the aromatization of n-butane observed on ZSM-5 (SiO₂/Al₂O₃ ratio of 80) alone. The catalytic performance of Mo₂C/ZSM-5 sensitively depended on its preparation and pretreatment. The selectivity of aromatics measured for pure ZSM-5 increased from 11-13% to 28-34% at the conversion level of 60-65%. The formation of aromatics was also observed over Mo₂C/SiO₂.     

A Novel Catalyst Pt/CoAl2O4/Al2O3 for Combination CO2 Reforming and Partial Oxidation of CH4

Pt/CoAl₂O₄/Al₂O₃, Pt/CoO_x/Al₂O₃, CoAl₂O₄/Al₂O₃ and CoO_x/Al₂O₃ catalysts were studied for combination CO₂ reforming and partial oxidation of CH₄. The results indicate that Pt/CoAl₂O₄/Al₂O₃ is the most effective, and XRD results indicate that Pt species are well dispersed over the Pt/CoAl₂O₄/Al₂O₃. High dispersion is related to the presence of CoAl₂O₄, formed during calcining at high temperature before Pt addition. In the presence of Pt, CoAl₂O₄ in the catalyst could be reduced partially at 973 K. Based on these results, it appears that zerovalent platinum with high dispersion and zerovalent cobalt resulting from CoAl₂O₄ reduction are responsible for high activity in the Pt/CoAl₂O₄/Al₂O₃ catalyst.     

Metal Exchanged ZSM-5 Zeolite Based Catalysts for Direct Decomposition of N2O

Co+Pt/ZSM-5 and Ag+Pt/ZSM-5 type catalysts were prepared by ion exchange method followed by calcination. These Co and Ag based catalysts, promoted by a small amount of Pt have been studied for their catalytic activity towards N₂O decomposition. Both the catalysts show high catalytic activity, however, cobalt–platinum based catalyst shows relatively better activity at higher temperature. At 550 °C almost 100% conversion of N₂O is achieved over Co+Pt/ZSM-5 with a maximum of 0.08479 mmole of N₂O decomposed per gram of the catalyst per unit time. These catalytic materials have been characterized for their structure, composition, morphology and other details, using XRD, SEM, EDX, ICP, BET techniques. Much improved catalytic activity for the bimetallic zeolite than the mono-metal containing compositions clearly demonstrate the synergistic effect of these transition metals, while high surface area of ZSM-5 is also responsible for the improved N₂O decomposition activity.     

Hydrodeoxygenation of dibenzofuran over noble metal supported on mesoporous zeolite

Hydrodeoxygenation has been considered to be one of the most promising methods for bio-oil upgrading. In this paper, the catalytic performance of noble metal supported on mesoporous zeolite in model bio-oil compound hydrodeoxygenation was examined. Dibenzofuran was chosen here because of its refractory nature and large molecular size. Our results indicate that Pt supported on mesoporous ZSM-5 show better performance in dibenzofuran hydrodeoxygenation than Pt/ZSM-5 and Pt/Al₂O₃. The excellent catalytic performance is attributed to the combination of strong acidity and mesopore structure in mesoporous zeolite.     

Pt-loaded P-MCM-41 as a novel bifunctional catalyst for catalytic combustion of trichloroethylene

Pt-loaded P-MCM-41 catalysts with different Si/P ratio were prepared and used as novel bifunctional catalysts for catalytic combustion of trichloroethylene (TCE). Acidic materials, ZSM-5, P-SiO₂ and Al₂O₃ as supports in Pt-loaded catalysts were also studied for comparison. The high activity for TCE conversion and low selectivity to tetrachloroethylene were observed on Pt/P-MCM-41 catalysts, indicating that phosphorus modified MCM-41 with an amount of weak Brønsted acid sites, in combination with Pt, was effective to form a bifunctional catalyst.     

Electrochemical lean-deNOx catalyst using H-conducting solid polymer electrolyte

The reduction of NO to N₂/N₂O in the presence of excess O₂ has been successfully achieved at 70 °C using an electrochemical cell of the type, 0.1% NO, 0–10% O₂, Pt | NAFION | Pt, H₂O. An H⁺-conducting solid polymer electrolyte (SPE) plays a key role in evolving hydrogen on the Pt cathode, where the catalytic NO–H₂ takes place. It was revealed that the competitive H₂–O₂ reaction is suppressed because the Pt surface was covered with stable nitrate (NO₃) species, which blocks oxygen adsorption hereon. The inhibition of H₂–O₂ reaction becomes most efficient at 100 °C in agreement with the optimal operation temperature range of SPE. The reduction efficiency of NO in an excess O₂ could be improved by packing 1 wt% Pt/ZSM-5 catalyst in the cathode room. The combination between the SPE cell and Pt catalysts can broadly be applied to novel low-temperature deNO_x processes in a strongly oxidizing atmosphere.     

Noble Metal (Pt, Rh, Pd) Promoted Fe-ZSM-5 for Selective Catalytic Oxidation of Ammonia to N2 at Low Temperatures

We have reported previously the excellent performance of Fe-exchanged ZSM-5 for selective catalytic oxidation (SCO) of ammonia to nitrogen at high temperatures (e.g., 400-500 °C). The present work indicates that the reaction temperature can be decreased to 250-350 °C when a small amount of noble metal (Pt, Rh or Pd) is added (by both doping and ion exchange) to the Fe-ZSM-5. The SCO activity follows the order: Pt/Fe-ZSM-5 > Rh/Fe-ZSM-5 > Pd/Fe-ZSM-5. The noble metal promoted Fe-ZSM-5 catalysts also show higher activity for NH₃ oxidation than Ce-exchanged Fe-ZSM-5 at low temperatures. On the Pt promoted Fe-ZSM-5, near 100% of NH₃ conversion is obtained at 250 °C at a high space velocity (GHSV = 2.3 × 10⁵ h^-1) and nitrogen is the main product. The presence of H₂O and SO₂ decreases the SCO performance only slightly. This catalyst is a good candidate for solving the ammonia slip problem that plagues the selective catalytic reduction (SCR) of NO with ammonia in power plants.