Abstract: Provided is a catalyst for production of unsaturated aldehyde and/or unsaturated carboxylic acid, which shows excellent mechanical strength and low attrition loss and is capable of producing the object product(s) at a high yield. The catalyst comprises a catalytically active component containing molybdenum, bismuth and iron as the essential ingredients, and inorganic fibers, and is characterized in that the inorganic fibers contain at least an inorganic fiber having an average diameter of at least 8 ?m and another inorganic fiber having an average diameter not more than 6 ?m.

Abstract: Disclosed is a method for producing a catalyst, in which physical properties of a dried material or a calcined material in a production process of the catalyst are stable and a change in at least one of a catalyst activity and a selectivity to a target product is small and hence reproducibility of the catalyst is excellent. The present invention is a method for producing a catalyst containing molybdenum, bismuth, and iron, which contains the steps of washing a surface of at least one device equipped in an apparatus for the production of catalyst, to which a solid matter adheres, with a basic solution, and producing the catalyst with the apparatus for the production of catalyst thus washed.

Abstract: An object of the present invention is to provide: a catalyst for production of acrylic acid which is a catalyst usable for production of acrylic acid and is excellent in the catalytic performances such as catalytic activity and in the physical properties such as physical strength of the catalyst itself; and a process for production of acrylic acid using this catalyst. As a means of achieving this object, a catalyst for production of acrylic acid according to the present invention is a catalyst obtained by drying a mixed liquid of starting materials including molybdenum and vanadium as essential components to give a dried material, molding the dried material with a liquid binder, and calcining the resultant molding, with the catalyst being characterized in that an ignition loss ratio of the dried material is from 5 to 40% by mass.

Abstract: The present invention relates to a complex oxide catalyst of Bi/Mo/Fe and an oxidative dehydrogenation of 1-butene in the presence of a catalyst herein. A catalyst of the present invention is superior to the conventional Bi/Mo catalyst in thermal and mechanical stabilities, conversion and selectivity toward 1,3-butadiene, while showing a long-term catalytic activity.

Abstract: A process for producing a ringlike oxidic shaped body by mechanically compacting a pulverulent aggregate introduced into the fill chamber of a die, wherein the outer face of the resulting compact corresponds to that of a frustocone.

Abstract: A method of preparing multicomponent bismuth molybdate catalysts composed of four metal components and a method of preparing 1,3-butadiene using the catalyst, and particularly, to multicomponent bismuth molybdate catalysts composed of a divalent cationic metal, a trivalent cationic metal, bismuth and molybdenum, a preparation method thereof, and a method of preparing 1,3-butadiene from a C4 mixture including n-butene and n-butane using oxidative dehydrogenation are described.

Abstract: This invention relates to a method of preparing a multicomponent bismuth molybdate catalyst by changing the pH of a coprecipitation solution upon coprecipitation and a method of preparing 1,3-butadiene using the catalyst. The multicomponent bismuth molybdate catalyst, coprecipitated using a solution having an adjusted pH, the preparation method thereof, and the method of preparing 1,3-butadiene through oxidative dehydrogenation using a C4 mixture including n-butene and n-butane as a reactant are provided. The C4 raffinate, containing many impurities, is directly used as a reactant without an additional process for separating n-butane or extracting n-butene, thus obtaining 1,3-butadiene at high yield. The activity of the multicomponent bismuth molybdate catalyst can be simply increased through precise pH adjustment upon coprecipitation, which is not disclosed in the conventional techniques.

Abstract: A process is provided for producing a complex oxide catalyst which exhibits superior catalytic activity in a vapor phase catalytic oxidation reaction, particularly in production of unsaturated aldehyde and unsaturated carboxylic acid. The process is characterized by the steps of preparing an aqueous slurry by mixing a complex oxide containing molybdenum and cobalt with an acid and water; drying the aqueous slurry; and calcining the resulting dried solid. Preferably, the complex oxide is obtained as follows: a molybdenum- and cobalt-containing complex oxide catalyst which has been used in a vapor phase catalytic oxidation reaction is mixed with an aqueous extracting solution obtained by dissolving at least one of ammonia and an organic base in water, to thereby extract molybdenum and cobalt into the aqueous phase; and the aqueous phase is dried and is then calcined under an atmosphere of an oxidizing gas.

Abstract: Mo-, Bi- and Fe-comprising multimetal oxide compositions of the general stoichiometry I, Mo12BiaCobFecKdSieOx??(I), where a=0.5 to 1, b=7 to 8.5, c=1.5 to 3.0, d=0 to 0.15, e=0 to 2.5 and x=the stoichiometric coefficient of O2? which guarantees the electric neutrality of the multimetal oxide, and 12?b?1.5·c=A and 0.5?A?1.5, 0.2?a/A?1.3, and 2.5?b/c?9, and the use thereof.

Abstract: An object of the present invention is to provide a catalyst exhibiting excellent performance particularly in partial oxidation reaction. Another object is to provide a method for efficiently producing carboxylic acid or carboxylic anhydride through vapor-phase partial oxidation of an organic compound by use of an oxygen-containing gas in the presence of the catalyst. The catalyst contains (1) diamond; (2) at least one species selected from among Group 5 transition element oxides, collectively called oxide A; and (3) at least one species selected from among Group 4 transition element oxides, collectively called oxide B. The method for producing a carboxylic acid or a carboxylic anhydride includes subjecting an organic compound to vapor phase partial oxidation by use of an oxygen-containing gas in the presence of the catalyst, wherein the organic compound is an aromatic compound having one or more substituents in a molecule thereof, the substituents each including a carbon atom bonded to an aromatic ring.

Abstract: A melt phase process for making a polyester polymer melt phase product by adding an antimony containing catalyst to the melt phase, polycondensing the melt containing said catalyst in the melt phase until the It.V. of the melt reaches at least 0.75 dL/g. Polyester polymer melt phase pellets containing antimony residues and having an It.V. of at least 0.75 dL/g are obtained without solid state polymerization. The polyester polymer pellets containing antimony residues and having an It.V. of at least 0.70 dL/g obtained without increasing the molecular weight of the melt phase product by solid state polymerization are fed to an extruder, melted to produce a molten polyester polymer, and extruded through a die to form shaped articles. The melt phase products and articles made thereby have low b* color and/or high L* brightness, and the reaction time to make the melt phase products is short.

Abstract: The invention relates to a bulk catalyst comprising at least 60 wt % metal oxidic particles comprising one or more Group VIII metals and Group VIB metal molybdenum, comprising less than 10 mole % of a second Group VIB metal and comprising a Group V metal in an amount less than 10 mole %, which bulk catalyst has been calcined at a temperature below a temperature where the hexagonal metastable crystal structure changes to an inactive crystalline structure, and which bulk catalyst has a metastable hexagonal phase characterized by an X-ray diffraction pattern having reflections at 33-35 and 58-61 °2?; and to a process for the manufacture of the bulk catalyst, to the corresponding sulphided bulk catalyst and to the use of said bulk catalyst or sulphided bulk catalyst in the hydroprocessing of a hydrocarbon feedstock.

Abstract: The present invention provides a preparation process of complex oxides catalyst containing Mo, Bi, Fe and Co, which comprising steps as following: dissolving precursor compounds of the components for catalyst and complexing agent in water to obtain a solution, and then drying, molding and calcining the solution to obtain catalyst. The catalyst is used for gas phase oxidation of light alkenes to unsaturated aldehydes. The catalyst has high activity, selectivity and stability. The reaction condition is mild. The preparation process of the catalyst is easy to operate and can be used for mass production.

Abstract: A process for producing geometric shaped catalyst bodies K whose active material is a multielement oxide of stoichiometry [BiaZ1bOx]p[BicMo12FedZ2eZ3fZ4gZ5hZ6iOy]1, in which a finely divided oxide BiaZ1bOx and, formed from element sources, a finely divided mixture of stoichiometry BicMo12FedZ2eZ3fZ4gZ5hZ6i are mixed in a ratio of p:1, this mixture is used to form shaped bodies and these are treated thermally, where 0<c?0.8.

Abstract: A catalyst for use in the production of an unsaturated aldehyde and/or an unsaturated carboxylic acid, the catalyst comparing (or, preferably, being composed of) a mixed oxide containing molybdenum, bismuth and iron, which has improved mechanical strength, is produced by a method including the steps of (1) drying an aqueous solution or an aqueous slurry containing raw materials of the catalyst and then firstly calcining a dried product in a molecular oxygen-containing gas atmosphere to obtain a calcined product; (2) heating the calcined product obtained in Step (1) in the presence of a reducing material to obtain a reduced product having a mass loss of 0.05 to 6%; and (3) secondly calcining the reduced product obtained in Step (2) in a molecular oxygen-containing gas atmosphere.

Abstract: A layered heterostructured coating has functional characteristics that enable the controlled release of volatile agents. The coating has photocatalytic properties, since it uses titanium dioxide, its derivatives or materials with similar photocatalytic properties (2), which upon solar irradiation open and/or degrade nano or microcapsules (3) and subsequently releases in a controlled form the volatile agents contained in them.

Abstract: Disclosed herein are mixed oxide catalysts for the catalytic gas phase oxidation of alkanes, or mixtures of alkanes and olefins, for the production of aldehydes and carboxylic acids with air or oxygen in the presence of inert gases at elevated temperatures and pressures, and methods for the production of the catalyst.

Abstract: According to at least one aspect of the present invention, a urea-resistant catalytic unit is provided. In at least one embodiment, the catalytic unit includes a catalyst having a catalyst surface, and a urea-resistant coating in contact with at least a portion of the catalyst surface, wherein the urea-resistant coating effectively reduces urea-induced deactivation of the catalyst. In at least another embodiment, the urea-resistant coating includes at least one oxide from the group consisting of titanium oxide, tungsten oxide, zirconium oxide, molybdenum oxide, aluminum oxide, silicon dioxide, sulfur oxide, niobium oxide, molybdenum oxide, yttrium oxide, nickel oxide, cobalt oxide, and combinations thereof.

Abstract: A catalyst is provided and includes fine catalyst particles of a composition represented by formula (1): PtuRuxTayTz, in which T is at least one element selected from the group consisting of Hf, W, Ni, and V; u, x, y, and z are 10 to 98.9 atm %, 0.1 to 50 atm %, 0.5 to 35 atm %, and 0.5 to 35 atm %, respectively, or formula (2): PtuRuxTayTz, in which T is at least one element selected from the group consisting of Ct, Mo, Nb, Zr, and T; u, x, y, and z are 40 to 70 atm %, 0.1 to 50 atm %, 0.5 to 15 atm %, and 0.5 to 15 atm %, respectively.

Abstract: A platinum alloy catalyst PtXY, wherein X is nickel, cobalt, chromium, copper, titanium or manganese and Y is tantalum or niobium, characterised in that in the alloy the atomic percentage of platinum is 46-75 at %, of X is 1-49 at % and of Y is 1-35 at %; provided that the alloy is not 66 at % Pt20 at % Cr14 at % Ta or 50 at % Pt, 25 at % Co, 25 at % Ta is disclosed. The catalyst has particular use as an oxygen reduction catalyst in fuel cells, and in particular in phosphoric acid fuel cells.

Abstract: The present invention relates to a method of preparing a heteropoly acid catalyst used for the production of methacrylic acid by gas phase oxidation of methacrolein, more precisely a method of preparing a heteropoly acid catalyst comprising the steps of preparing a slurry by adding metal precursors and ammonium salt to protonic acid Keggin-type heteropoly acid aqueous solution and stirring thereof; and drying, molding and firing the slurry to give a catalyst. The present invention provides a method of preparing a heteropoly acid catalyst exhibiting high methacrolein conversion rate and methacrylic acid selectivity without pre-firing process by using high purity protonic acid Keggin-type heteropoly acid and ammonium salt.

Abstract: An oxide catalyst composition comprising the elements molybdenum, vanadium, niobium and titanium and a process for making the catalyst composition. A process for the selective oxidation of ethane and/or ethylene to acetic acid using the catalyst composition. The catalyst composition provides high selectivity to acetic acid with reduced selectivity to ethylene.

Abstract: A method of preparing a catalyst for producing acrolein by oxidation of propylene at high space velocity, said catalyst is a Mo—Bi—Fe—Co based composite metal oxide. Producing unsaturated aldehyde via partial oxidation of lower unsaturated olefin at high space velocity using said catalyst is suitable for process with or without off-gas recirculating. Said catalyst is prepared by co-precipitation, the reaction conditions for using said catalyst to produce unsaturated aldehyde are, the space velocity of unsaturated lower olefin relative to catalyst being 120˜200 h-1(STP), reaction temperature being 300˜420° C. and absolute pressure being 0.1˜0.5 MPa; a single-stage unsaturated lower olefin conversion ratio of greater than 98.0% and carbon oxide yield of less than 3.3% with an overall yield of unsaturated lower aldehyde and acid of greater than 94.0% are obtained. The process to prepare the said catalyst is simple, easy to be repeated, and capable of industrial scale-up.

Abstract: A catalyst system for the reduction of NOx comprises a catalyst comprising a metal oxide catalyst support, a catalytic metal oxide comprising at least one of gallium oxide or silver oxide, and at least one promoting metal selected from the group consisting of silver, cobalt, molybdenum, tungsten, indium, bismuth and mixtures thereof. The catalyst system further comprises a gas stream comprising an organic reductant, and a compound comprising sulfur. A method for reducing NOx utilizing the said catalyst system is also provided.

Abstract: The invention relates to a process for recovering Group VIB metals from a catalyst, in particular a spent bulk catalyst, comprising one or more Group VIB metals and one or more Group VIII metals. Further, the invention relates to a solid Group VIB metal compound obtainable by the process according to the invention having the general formula H2XO4, wherein X=W1-yMoy, wherein y is between 0 and 1 and to its use in a process for the manufacture of a fresh catalyst.

Abstract: The present invention relates to a heteropoly acid catalyst which is used for the production of methacrylic acid by gas phase oxidation of methacrolein and a preparing method thereof. The present invention, thereby, provides a novel heteropoly acid catalyst having excellent methacrolein conversion rate, methacrylic acid selectivity and yield.

Abstract: Alkenes, unsaturated saturated carboxylic acids, saturated carboxylic acids and their higher analogues are prepared cumulatively from corresponding alkanes utilizing using a multi-staged catalyst system and a multi-stage process which comprises steam cracking of alkanes to corresponding alkenes at flame temperatures and at short contact times in combination with one or more oxidation catalysts for catalytically converting the corresponding alkenes to further corresponding oxygenated products using short contact time reactor conditions.

Abstract: The present invention provides a Mo—Bi—Nb based composite metal oxide (with the proviso that Te is not included); a method for producing (meth)acrylic acid from at least one reactant selected from the group consisting of propylene, propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, in which a Mo—Bi—Nb based composite metal oxide (with the proviso that Te is not included) is used as a catalyst; and a reactor used for producing (meth)acrylic acid from at least one reactant selected from the group consisting of propylene, propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, in which a Mo—Bi—Nb based composite metal oxide (with the proviso that Te is not included) is used as a catalyst. Further, the present invention provides a method for producing the (meth)acrylic acid without any additional process of converting (meth)acrolein into (meth)acrylic acid.

Abstract: The invention relates to mixed oxide catalysts for the catalytic gas-phase oxidation of olefins and methylated aromatics, processes for producing the catalysts and the reaction with air or oxygen in the presence of inert gases in various ratios at elevated temperatures and pressure to form aldehydes and carboxylic acids.

Abstract: This invention relates to a bismuth molybdate catalyst, a preparation method thereof, and a method of preparing 1,3-butadiene using the same, and to a bismuth molybdate catalyst, a preparation method thereof, and a method of preparing 1,3-butadiene using the same, in which 1,3-butadiene can be prepared through oxidative dehydrogenation directly using a C4 mixture including n-butene and n-butane as a reactant in the presence of a mixed-phase bismuth molybdate catalyst including ?-bismuth molybdate (Bi2Mo3On) and ?-bismuth molybdate (Bi2MoO6). According to this invention, the C4 raffinate, containing many impurities, is used as a reactant, without an additional n-butane separation process, thus obtaining 1,3-butadiene at high yield.

Abstract: Methods for synthesizing dimeric or polymeric reaction products of nitrogen aromatics comprise contacting a composition comprising the nitrogen aromatic with a catalyst composition. The catalyst comprises a first metal substrate having a second reduced metal coated on the substrate.

Abstract: The present invention relates to the novel catalytic composition having a high specific activity in reactions involving hydroprocessing of light and intermediate petroleum fractions, and preferably in hydrodesulphurization and hydrodenitrogenation reactions. The inventive catalyst contains at least one element of a non-noble metal from group VIII, at least one element from group VIB and, optionally, a group one element of the VA group, which are deposited on a novel catalytic support comprising of an inorganic metal oxide from group IVB, consisting of an (1D) one-dimensional nanostructured material having nanofibers and/or nanotube morphology with high specific surface area of between 10 and 500 m2/g.

Abstract: A catalyst for producing acrolein and/or acrylic acid from propylene by gas-phase catalytic oxidation with molecular oxygen-containing gas, comprising a catalytic active component containing molybdenum, bismuth and cobalt as essential elements, and having a crystallinity T of 4% or more and 18% or less in the 2? range of 5° to 90°, measured by an X-ray diffraction analysis with Cu—K? radiation; and a process for producing acrolein and/or acrylic acid by gas-phase catalytic oxidation of propylene with molecular oxygen, comprising the step of conducting the gas-phase catalytic oxidation in the presence of the catalyst. According to the catalyst and the process for producing acrolein and/or acrylic acid of the present invention, it is possible to stably produce acrolein and/or acrylic acid at a high yield for a long period.

Abstract: A catalyst composition for dehydration of an alcohol to prepare an alkene is provided. The catalyst composition comprises a catalyst and a modifying agent which is phosphoric acid, sulfuric acid or tungsten trioxide, or a derivative thereof. A process for preparing an alkene by dehydration of an alcohol is also provided. The process comprises mixing one or more alcohols and optionally water and the catalyst composition.

Abstract: A method for the production of a nanocrystalline bismuth-molybdenum mixed oxide, the use of the bismuth-molybdenum mixed oxide as catalyst for chemical conversions, in particular for a conversion of propylene to acrolein and/or acrylic acid or of isobutylene to methacrolein and/or methacrylic acid, as well as a catalyst that contains the bismuth-molybdenum mixed oxide.

Abstract: The present invention comprises a method for preparing a mixed oxide catalyst for use in producing acrylonitrile or methacrylonitrile from propane or isobutene by ammoxidation in a gaseous phase via methods of heating or calcining precursor solid mixture to obtain mixed metal oxide catalyst compositions that exhibit catalytic activity.

Abstract: A process is provided for producing a complex oxide catalyst which exhibits superior catalytic activity in a vapor phase catalytic oxidation reaction, particularly in production of unsaturated aldehyde and unsaturated carboxylic acid. The process is characterized by the steps of preparing an aqueous slurry by mixing a complex oxide containing molybdenum and cobalt with an acid and water; drying the aqueous slurry; and calcining the resulting dried solid. Preferably, the complex oxide is obtained as follows: a molybdenum- and cobalt-containing complex oxide catalyst which has been used in a vapor phase catalytic oxidation reaction is mixed with an aqueous extracting solution obtained by dissolving at least one of ammonia and an organic base in water, to thereby extract molybdenum and cobalt into the aqueous phase; and the aqueous phase is dried and is then calcined under an atmosphere of an oxidizing gas.

Abstract: A catalyst composition for use in manufacturing methacrolein by reacting with one of isobutene and t-butanol, the catalyst composition being represented by the formula of: x (Mo12BiaFebCocAdBeOf)/y Z. Mo12BiaFebCocAdBeOf is an oxide compound. Z is a catalyst carrier is one of graphite, boron, silicon, germanium powder, and a mixture thereof. Mo, Bi, Fe, Co, and O are chemical symbols of molybdenum, bismuth, iron, cobalt, and oxygen respectively. A is one of W, V, Ti, Zr, Nb, Ni, and Re. B is one of K, Rb, Cs, Sr, and Ba. The catalyst is adapted to not only enhance the production of methacrolein with high activeness and high selectivity but also effectively control the heat point of the catalyst during the methacrolein manufacturing process to prolong the catalyst life.

Abstract: The present invention relates to an improved catalyst for direct conversion of methane to ethane and ethylene, a method for producing the catalyst and a process making use of the catalyst.

Abstract: The invention relates to a coated catalyst, which is obtainable from a catalyst precursor comprising (a) a support body, (b) a coating comprising (i) a catalytically active, multimetal oxide which comprises molybdenum and at least one further metal and is of the general formula (I) Mo12BiaCrbX1cFedX2eX3fOy??(I) where X1=Co and/or Ni, X2=Si and/or Al, X3=Li, Na, K, Cs and/or Rb, 0.2?a?1, 0?b?2, 2?c?10, 0.5?d?10, 0?e?10, 0?f?0.5 and y=a number which, with the prerequisite of charge neutrality, is determined by the valency and frequency of the elements in (I) other than oxygen, and (ii) at least one pore former.

Abstract: A method for producing a catalyst by contacting a mixed metal oxide catalyst with water, and optionally, an aqueous metal oxide precursor to produce a modified mixed metal oxide, and calcining the modified mixed metal oxide.

Abstract: An object of the present invention is to provide a molding and a method for producing the same; a catalyst for the production of an unsaturated aldehyde and an unsaturated carboxylic acid, and a method for producing the same; and a catalyst for the production of methacrylic acid, and a method for producing the same. The molding of the present invention shows a shape including a plurality of columnar portions disposed with a predetermined gap; and bridge portions which are provided at both ends in longitudinal directions of two adjacent columnar portions and join adjacent columnar portions each other; and including through holes surrounded by a plurality of columnar portions in the longitudinal directions of the columnar portions, and openings formed on a peripheral surface by a gap between the plurality of adjacent columnar portions.

Abstract: The invention relates to mixed oxide catalysts made of hollow shapes for the catalytic gas phase oxidation of olefins, and to a method for producing the catalysts by applying them as a layer to a carrier made of organic material and removing said organic material. The reaction into aldehydes and carboxylic acids occurs by air or oxygen in the presence of inert gases in different quantity ratios, at elevated temperatures and pressure in the presence of said catalysts.

Abstract: The invention relates to soluble metal oxides and mixed metal oxides and to solutions comprising metal oxides and mixed metal oxides. The invention further relates to a process for preparing a soluble metal oxide and a soluble mixed metal oxide and additionally relates to a process for modifying the solubility of a soluble metal oxide. The metal oxides, mixed metal oxides and solutions thereof have a number of applications and in particular are suitable for use as catalysts and also as precursors for the formation of metal films.

Abstract: A catalyst is provided having higher mercury oxidation performance than a conventional catalyst without increasing catalyst quantity or enhancing SO2 oxidation performance and constitutes an oxidation catalyst for metal mercury, which contains a molybdenum and vanadium complex oxide, for example, MoV2O8, as a main component having a catalytic activity and is formed by placing the molybdenum and vanadium complex oxide in layers only on the surface of a plate-like or honeycomb-like porous carrier. The porous carrier contains Ti and W and has a function of an NOx removal catalyst as a whole.

Abstract: The present invention relates to a catalyst system, an oxidation reactor comprising the same, and a method for producing an acrolein and an acrylic acid by using the same. By using the catalyst system according to the present invention, when acrolein and acrylic acid are produced, since heat accumulation in a catalyst layer may be effectively prevented, catalyst deterioration may be prevented, and the catalyst may be stably used for a long period of time. In addition, an acrolein and an acrylic acid may be produced at high selectivity and high yield.

Abstract: A nanoporous metal oxide material comprising two or more metal oxides, wherein the nanoporous metal oxide material has ceria content of 10 to 60 weight %, zirconia content of 20 to 90 weight %, and alumina content of 70 weight % or less, and has nanopores whose diameters are 10 nm or less, and the metal oxides are homogeneously dispersed in a wall constituting the nanopores.

Abstract: The invention relates to mixed oxide catalysts for the catalytic gas phase oxidation of alkanes, or mixtures of alkanes and olefins, for the production of aldehydes and carboxylic acids with air or oxygen in the presence of inert gases at elevated temperatures and pressure, and a method for the production of catalysts.

Abstract: A process for making a porous catalyst, comprises a) providing an aqueous solution containing a nanoparticle precursor, b) forming a composition containing nanoparticles, c) adding a first catalytic component or precursor thereof and a pore-forming agent to the composition containing nanoparticles and allowing the first catalytic component, the pore-forming agent, and the nanoparticles form an organic-inorganic structure, d) removing water from the organic-inorganic structure; and e) removing the pore-forming agent from the organic-inorganic structure so as to yield a porous catalyst.

Abstract: A catalyst for acrylonitrile synthesis is disclosed which is composed of particles containing silica and a composite oxide including at least molybdenum. When the Mo/Si atomic ratio in bulk composition of the catalyst is represented by A and the Mo/Si atomic ratio in surface composition of the particles is represented by B, B/A is not more than 0.6.