Masakazu Iwamoto

Novel catalytic decomposition and reduction of NO

Nitrogen monoxide (NO) is thermodynamically unstable relative to Nz and O2 at low tempera~res, and therefore its catalytic decomposition is the simplest and cheapest method for the removal of NO from exhaust streams [ l-51. To date, however, no suitable catalyst of consistently high activity has been found, except for a few described later. Most previous attempts to develop practical decomposition catalysts have dealt with noble metals and metal oxides. Some of these materials are active in the reduced state, but oxygen contained in the feed gas or released by the decomposition of NO competes with NO for the adsorption sites and poisons the activity. To remove surface oxygen and regenerate catalytic activity, high reaction temperatures and/or gaseous reductants are required. Thus, catalytic reduction processes using NH,, HC or CO have been applied for removing NO. In the present catalytic reduction processes, selective and non-selective methods are used in industrial boilers and vehide engines, respectively. Many books and reviews [4-lo] have described the details of these processes. Here the disadvantages or problems that each of the present reduction processes suffers are summarized [ 91. (a) In the selective catalytic reduction system on V,OS-TiO,-W03 with ammonia as a reductant there are several disadvantages such as high costs of facilities and inning and leakage of unreacted ~monia. (b) The automobile catalytic converter is the only technology available for meeting the most stringent emission standards. In this technology Pt-Pd-Rh catalysts are preferentially used with several limitations such as using unleaded gasoline and maintaining a specified air/fuel ratio. However, this system cannot meet the requirements of newly developed engines in which the air/fuel ratio has been made lean to an air-rich region, because the exhaust contains a considerable amount of oxygen and the present three-way catalysts do not work under such conditions.

Heterogeneous catalysis for removal of NO in excess oxygen. Progress in 1994

Abstract The progress of catalytic decomposition of NO (and N 2 O) and selective catalytic reduction of NO by hydrocarbons in the presence of excess oxygen in the past year (1994) have been summarized. There are many reports and suggestions for the active catalysts and the reaction mechanisms in both reaction systems. Several problems, however, remain to be solved at present; for example, enhancement of the catalytic activity, improvement of the life time, suppression of the formation of the harmful by-products and clarification of the reaction mechanisms.

Highly effective acetalization of aldehydes and ketones with methanol on siliceous mesoporous material

Aromatic and linear aldehydes as well as cyclohexanone could be converted to the corresponding dimethylacetals in yields of ca. 90–100% at ambient or refluxing temperature in the titled reaction.

Pronounced catalytic activity of Fe0.08Cs2.5H1.26PVMo11O40 for direct oxidation of propane into acrylic acid

Abstract Fe 3+ or Ni 2+ -substitution for H + and V 5+ -substitution for Mo 6+ in Cs 2.5 H 0.5 PMo 12 O 40 greatly enhanced the catalytic activity for direct oxidation of propane into acrylic acid. Of the catalysts tested Cs 2.5 Fe 0.08 H 1.26 PVMo 11 O 40 gave the highest yield of acrylic acid, 13%.

Zeolites in Environmental Catalysis

Publisher Summary The role of catalysis in environmental improvement is crucial. The environmental catalysis can be categorized into five categories: (1) control of emissions of environmentally unacceptable compounds, especially in flue gases and car exhaust gases, (2) conversion of solid or liquid waste into environmentally acceptable products, (3) selective manufacture of alternative products that can replace environmentally harmful compounds, such as some chlorofluorocarbons (CFCs), (4) replacement of environmentally hazardous catalysts in existing processes, and (5) development of catalysts that enable new technological routes to valuable chemical products without the formation of polluting byproducts. Zeolites are potential catalysts because of the characteristic pore structures, acidic properties, and ion-exchange properties. Zeolites and related microporous materials are one class of solid catalysts that play an increasing role when developing strategies for better environment. The chapter discusses the use and potential of zeolite catalysts in the emission control of undesirable compounds and waste avoidance. It also describes the way in which the catalytic activities of copper ion-exchanged zeolites depend on the zeolite structure and the exchange level of copper ion.

Performance and durability of Pt-MFI zeolite catalyst for selective reduction of nitrogen monoxide in actual diesel engine exhaust

Abstract Selective catalytic reduction of nitrogen monoxide (NO) by hydrocarbon in an oxidizing atmosphere has been studied over platinum-MFI zeolite (Pt-MFI) in synthesized or actual diesel engine exhaust gases. The activity of Pt-MFI in the synthesized gas, containing 10% water, changed in the early stage of the use, leveled off after 150–200 h, and remained constant for more than 800 h. The Pt-MFI catalyst also showed stable activity at 423–773 K and 10 000–150 000 h − (gas hourly space velocity) in actual engine exhaust with light oil as a fuel. The degree of nitrogen monoxide reduction increased linearly upon addition of ethylene into the exhaust gas.

Selective catalytic reduction of no by ethene in excess oxygen over platinum ion-exchanged MFI zeolites

Abstract Various noble metal ion-exchanged MFI zeolites have been examined as catalysts for the selective reduction of NO by ethene in the presence of excess oxygen. Of the catalysts ion-exchanged for Ru, Rh, Pd, Ir, and Pt, Pt-MFI zeolite showed the highest catalytic activity for the conversion of NO into N2. The catalytic activity was not reduced upon the addition of 8.6 vol.-% water vapor or 300 ppm sulfur dioxide in the reactant stream. It was hardly changed during the continuous experiment of 1000 h except for the initial period of use, indicating the high durability of Pt-MFI. Temperature-programmed decomposition and dynamic XRD measurements over Pt-MFI revealed that metallic platinum particles were formed through the decomposition of tetraammineplatinum ion during the pre-treatment around 673 K in helium atmosphere. The sizes of platinum particles were confirmed by TEM to be about 3 and 13 nm and did not change after use in the catalytic run.

Reversible and irreversible adsorption of nitrogen monoxide on cobalt lon-exchanged ZSM-5 and mordenite zeolites at 273–523 K

The adsorbability of nitrogen monoxide (NO) on cobalt ion-exchanged zeolites has been studied by pressure swing adsorption (PSA), temperature-programmed desorption (TPD) and IR techniques on the following zeolite samples; ZSM-5, mordenite, ferrierite, offretite/erionite, L-, Y- and X-type. The amounts of NO reversibly (q*rev) and irreversibly (q*irr) adsorbed at 273 K per cobalt ion exchanged, increased with decreasing aluminium content of the parent zeolite. On Co-ZSM-5 zeolite, both q*rev and q*irr were constant, independent of the ion exchange level. Over the range 273–523 K the maximum amount of reversible adsorption on Co-ZSM-5 or Co-mordenite has been observed at around 323–473 K, while the amount of irreversible adsorption decreased monotonically with increasing adsorption temperature. It has been confirmed on Co-ZSM-5 that most of the reversible adsorbates at 298 K are NO2+. The irreversibly adsorbed NO species on Co-ZSM-5 have been attributed to two kinds of dinitrosyl adsorbates. One has an ON—Co—NO bond angle of 99° and desorbs around 390 K, while the bond angle of the other is 123° and the desorption temperature is ca. 510 K. On mordenite and Y-type zeolites only the latter species was observed.

Selective Catalytic Reduction of no by Hydrocarbon in Oxidizing Atmosphere

Abstract In the presence of O 2 , SO 2 , and H 2 O selective reduction of NO by hydrocarbon over various catalysts, especially, over copper ion-exchanged zeolite has been studied. Simultaneous presence of O 2 and hydrocarbon such as ethene, propene, and propane with NO in the reactant gas resulted in the great enhancement of the catalytic activity for the removal of NO at low temperature (473–673 K). On the other hand, the addition of CO, H 2 , or CH 4 to the NO+O 2 system did not cause any selective reduction of NO. In the former selective reduction, the increment of concentration of hydrocarbon increased the conversion into N 2 and expanded the active temperature region. Addition of oxygen to reactant stream is necessary to achieve the selective reduction of NO, and with Cu-MFI zeolite the maximum activity was observed in the range of oxygen concentration of 0.8–2.0%. No deterioration in the catalytic activity was observed at 573 K even after 30 h of continuous service. When SO 2 or H 2 O was added to NO–O 2 +hydrocarbon gas stream, a certain decrement in the catalytic activity of Cu-MFI zeolites was observed. Within the present experiments, the activity was restored in its absence. Various metal ion-exchanged zeolites, metal loading alumina, and oxides have been screened as catalysts for the reaction and it was clarified that Cu-MFI zeolite catalysts are the most active at high SV region. The addition of copper to zeolites, alumina, and silica-alumina greatly enhanced the activities.

Enhancement of catalytic activity of Cs2.5Ni0.08H0.34PMo12O40 by V5+-substitution for oxidation of isobutane into methacrylic a

Abstract V5+-substitution for Mo6+ in Cs2.5Ni0.08H0.34PMo12O40 increased the yields of methacrylic acid and methacrolein. The maximum yields were obtained for the mono-V5+-substituted heteropoly compound, Cs2.5Ni0.08H1.34PVMo11O40.