2287results about "Heterogenous catalyst chemical elements" patented technology

The invention provides a novel acrylonitrile catalyst and a preparation method thereof. The novel acrylonitrile catalyst is prepared from the following raw materials: mixed salt, an active component, silica sol, a rare earth precursor, a carrier and a cosolvent, by introducing the cosolvent and optimizing the carrier structure, the dispersity of the rare earth precursor is improved, the production process is optimized, the doping efficiency of the rare earth precursor is remarkably improved, the activity, selectivity and stability of the novel acrylonitrile catalyst are improved, generation of by-products CO, CO2, acrolein and acrylic acid during acrylonitrile production can be reduced, and industrial efficient preparation is achieved.

The invention discloses a high-entropy oxide for synergic nitrogen removal and catalysis as well as a preparation method and application thereof, and belongs to the technical field of material preparation, the high-entropy oxide is a single solid solution phase formed by five or more metal elements of Fe, Co, Ni, Cu, Mn, Ti and Ce and an oxygen element, the configuration entropy of the high-entropy oxide is greater than or equal to 1.5 R, R is a gas constant, and R is an oxygen constant. The mole fraction of each metal element is 0.1-0.3, and the sum of the mole fractions of the metal elements is 1. According to the high-entropy oxide with the synergistic nitrogen removal and catalysis effects and the preparation method and application thereof, a synergistic catalysis system is constructed through the high-entropy oxide and silicon carbide, and the high-entropy oxide has the multiple advantages of being high in nitrogen removal efficiency, high in stability, simple in process, environmentally friendly and wide in application range; the removal rate of total nitrogen and key nitrogen pollutants can reach 90% or above in the seawater high-salt environment, and the environment-friendly emission requirement is met.

Disclosed are high-entropy oxides, and methods of their preparation. The high-entropy oxide is characterised by a sub-micron particle size and rod-like particle shape. The method of its preparation includes a co-precipitation step, preferably using an oxalate compound as a precipitating agent. Also disclosed are an electrode, e.g. an anode, a catalyst and an electrochemical cell comprising the high-entropy oxide.

The invention discloses a large-aperture aluminum oxide loaded copper-based catalyst as well as preparation and application thereof. The large-aperture alumina-loaded copper-based catalyst comprises a large-aperture alumina carrier, and copper oxide and lanthanum oxide loaded on the surface of the large-aperture alumina carrier, the large-aperture alumina-loaded copper-based catalyst is granular, the specific surface area is 250-500 m < 2 > / g, the pore volume is 1.0-2.0 cm < 3 > / g, the average aperture is 16-30 nm, and the pore diameter of the large-aperture alumina-loaded copper-based catalyst is 20-30 nm. The large-aperture alumina supported copper-based catalyst comprises the following components in percentage by mass: 79%-98.9% of a large-aperture alumina carrier, 0.1%-6% of copper oxide and 1%-15% of lanthanum oxide. The large-aperture aluminum oxide loaded copper-based catalyst disclosed by the invention shows relatively high catalytic activity and higher alcohol selectivity in a reaction for preparing higher alcohol from ethanol, and particularly has relatively high C6-C10 fatty alcohol selectivity.

Cu-based catalysts with excellent thermal stability for selective hydrogenation and a preparation method thereof are provided. The method includes: first, six mixed metal salts are instantaneously nucleated in an alkaline solution by the nucleation / crystallization isolation method, to prepare high-entropy composite metal hydroxides (H-LDHs) with uniform element distribution and similar metal proportions. Furthermore, well-crystallized high-entropy oxides (HEOs) are obtained based on the structural topology characteristics of H-LDHs, and a series of Cu-Mx / HEOs catalysts with flexible adjustable catalytic microzone geometries and electronic structures are obtained using the HEOs as precursors.

The invention discloses an adsorbent / catalyst based on waste lithium battery recovery and a preparation method and application thereof, and the preparation method comprises the following steps: discharging and disassembling a waste lithium battery, mixing and ball-milling the obtained positive electrode material, metal scrap, PVC and negative electrode graphite material, adding water in the ball-milling process, and carrying out mechanochemical reaction; and after the ball milling is finished, carrying out water leaching treatment on a ball milling product, drying filter residues after the water leaching treatment, and calcining in an inert atmosphere at the calcining temperature of 350-900 DEG C for 0.5-4 hours to obtain the pollutant removal adsorbent / catalyst. The process flow is completed at normal temperature and normal pressure by adopting a mechanochemical method, high-temperature operation is not needed, and the problem of high energy consumption of pyrometallurgy is avoided. Meanwhile, strong acid or strong alkali is not used, no waste liquid or toxic gas is discharged, and compared with a traditional wet metallurgy / wet modified adsorbent / catalyst process, a resource recovery and material preparation technology which is more environmentally friendly and conforms to the green and low-carbon concept is achieved.

The invention discloses a high-oxygen-storage zirconium solid solution material and a preparation method, and belongs to the technical field of rare earth catalytic materials, and the method comprises the following steps: precursor preparation, ultrasonic dispersion, double-gradient precipitation, ultrasonic aging, solid-liquid separation, three-section roasting and furnace cooling. Through the synergistic effect of double-gradient precipitation and ultrasonic aging, coarse grains and non-uniform particle size distribution are avoided, and the material is not prone to abnormal growth of the grains and structural collapse in long-term high-temperature service. Meanwhile, according to the gradient roasting process, through step-by-step regulation and control of crystal densification and crystal lattice reconstruction, separation of a fluorite phase and a pyrochlore phase easily occurring in traditional low-temperature single-section roasting is reduced, a stable crystal phase structure is maintained, it is ensured that the material can still keep sufficient active surface and pore channel structures under the working conditions of high temperature and thermal shock alternation, and the performance of the material is improved. The oxygen storage capacity and the long-term durability of the catalyst carrier are obviously improved.

This invention discloses a method for preparing a CuZnAlGa-based layered double hydroxide (TLH)-derived catalyst for methanol production from carbon dioxide-rich syngas. Using Cu, Zn, Al, and Ga metal salts as precursors, Na₂CO₃ and NaOH as precipitants, and a mixed alcohol-water solution as an auxiliary solvent, co-precipitation is performed under controlled temperature and pH to obtain a LDH-like catalyst precursor. After high-temperature calcination and in-situ reduction in a hydrogen atmosphere, a layered framework structure of Cu nanoparticles immobilized by oxides is obtained. The LDH-like structure provides lattice confinement, preventing Cu particle aggregation, and the interaction between Cu and the oxides enhances the catalyst surface's adsorption capacity for CO and CO₂, thereby improving the activity and stability of methanol production from carbon dioxide-rich syngas.

The invention discloses a large-aperture composite oxide catalyst, a preparation method thereof and a method for preparing higher alcohol from ethanol. The large-aperture composite oxide catalyst comprises copper oxide, lanthanum oxide and aluminum oxide. The large-aperture composite oxide catalyst is prepared by a coprecipitation method, and a nonionic surfactant is added as a pore-enlarging agent in the preparation process. The invention provides a method for preparing higher alcohol from ethanol, a reaction device adopted by the method comprises a main reactor and an auxiliary reactor which are sequentially connected in series, the main reactor is filled with the large-aperture composite oxide catalyst in the first aspect, the auxiliary reactor is filled with a Cu-Zn-Al composite oxide catalyst for aldehyde ester hydrogenation, and the Cu-Zn-Al composite oxide catalyst is used for hydrogenation of higher alcohol. According to the method, the ethanol conversion rate and the yield of high-carbon fatty alcohol with more than C6 are improved.

The invention provides a composite metal oxide catalyst, a preparation method thereof and a methane catalytic cracking method. The catalyst comprises 10%-80% of a dehydrogenation main active component, 5%-50% of a dehydrogenation auxiliary active component and the balance of a carrier, the period of metal elements in the dehydrogenation auxiliary active component comprises at least one of a fourth period, a fifth period and a sixth period, and the group of the metal elements in the dehydrogenation auxiliary active component comprises at least one of an IB group, a VB group, a VIB group and a VIIB group; and / or the metal elements in the dehydrogenation auxiliary active component comprise La series metal; the raw material of the composite metal oxide catalyst comprises a nonionic surfactant. The invention also provides a preparation method of the catalyst and a methane catalytic cracking method using the catalyst. The composite metal oxide catalyst is high in active metal dispersity, long in service life and relatively high in methane conversion rate, and the produced carbon nanotubes are good in quality.

Methods for making titanated silica supports, titanated chromium / silica pre-catalysts, and activated titanated chromium / silica catalysts are disclosed in which hydrogen peroxide and an alkali metal precursor are used during catalyst preparation. Resulting titanated chromium / silica pre-catalysts often contain silica, 0.1 to 5 wt. % chromium, 0.1 to 10 wt. % titanium, and less than or equal to 4 wt. % carbon, and further contain an alkali metal or zinc at a molar ratio of alkali metal:titanium or zinc:titanium from 0.02:1 to 3:1 and / or at an amount in a range from 0.01 to 2 mmol of alkali metal or zinc per gram of the silica. High melt index potential activated titanated chromium / silica catalysts can be used to polymerize olefins to produce, for example, ethylene based homopolymers and copolymers having HLMI values of greater than 30 g / 10 min.

The invention discloses a preparation method of a high-selectivity and high-strength methanol synthesis catalyst, and belongs to the technical field of catalysts. The method adopts a three-step precipitation method to prepare a catalyst precursor, specifically, after zirconium and aluminum form a precipitate 1 together, zinc continues to precipitate on the basis of the precipitate 1 to form a precipitate 2, and finally copper, zinc and aluminum continue to precipitate on the basis of the precipitate 2. The finally prepared methanol synthesis catalyst has excellent selectivity and strength while having low-temperature activity and stability. The methanol synthesis catalyst prepared by the method can be widely applied to methanol synthesis devices with annual output of 600,000 tons and above.

The present invention discloses a pretreatment method and application of an alumina-supported copper oxide-rare earth metal oxide catalyst. The pretreatment method is as follows: adding the alumina-supported copper oxide-rare earth metal oxide catalyst used for the reaction of ethanol to higher alcohols into a mixture of one or several C1-C8 alcohols, impregnating at 10-90 °C for 1-24 h, filtering to remove the excess alcohol after impregnation is completed, and then drying in an oven at 40-200 °C for 1-24 h to complete the pretreatment of the catalyst. The present invention provides the application of the alumina-supported copper oxide-rare earth metal oxide catalyst pretreated by the pretreatment method in the reaction of ethanol to higher alcohols. The pretreatment method of the present invention significantly increases the selectivity of the product higher alcohols and keeps the conversion rate of ethanol unchanged or slightly improved, thus solving the problem that it is difficult to balance both the conversion rate and selectivity in the prior art.

The invention provides a catalyst for preparing methanol through carbon dioxide hydrogenation and a preparation method of the catalyst. The catalyst is prepared from an active component and an auxiliary agent and / or a modifier, the active component is CuO or In2O3; the auxiliary agent is one or more of ZnO (zinc oxide), ZrO2 (zirconium oxide) and Al2O3 (aluminum oxide); and the modifying agent is one or more of La2O3, Y2O3 and CeO2. The catalyst is prepared by adopting a single-step coprecipitation method, the preparation process is greatly simplified, the preparation cost is greatly reduced, the large-scale production potential is achieved, the CO2 catalytic efficiency can be improved by 1-5%, and the methanol yield can be improved by 1-10%. The composition of the catalyst can be flexibly regulated and controlled, various catalysts with excellent performance can be obtained, and the most suitable catalyst can be conveniently selected according to the working condition environment in actual production.

A catalyst and methods for making the catalyst are provided. An exemplary catalyst includes the formula: MoaVbTec-TadOx. In this formula, a is 1.0, b is about 0.01 to about 0.3, c is about 0.01 to about 0.09, d is about 0.01 to about 0.05, and x is the number of oxygen atoms necessary to render the catalyst electronically neutral.

The nano titanium oxide main body photocatalytic sterilization multi-element material provided by the invention comprises 85%-98% of a nano titanium oxide material, 2%-15% of a perovskite material and a modifier, the modifier comprises silver, silver oxide and graphene, and the modifier comprises a nano titanium oxide main body and a nano titanium oxide main body. The nano titanium oxide main body photocatalytic sterilization multi-element material can fully utilize the characteristics of a perovskite structure material, overcomes the defects of a nano titanium oxide material, improves the light utilization rate, inhibits carrier recombination, improves the antibacterial durability, can utilize ultraviolet light to carry out catalytic sterilization and can also utilize ions to carry out sterilization, and the antibacterial effect is good. Sterilization can be achieved through the photolysis reaction of visible light, the synergistic composite sterilization effect is achieved, harmful germs are rapidly and effectively killed, the environment is kept fresh and safe, and the comprehensive sterilization and deodorization effect can be achieved by adding the modifier; the preparation method of the nano titanium oxide main body photocatalytic sterilization multi-element material provided by the invention is simple in steps, convenient to operate and easy to implement.

The invention discloses a catalyst for preparing gamma-butyrolactone through liquid phase dehydrogenation of 1, 4-butanediol as well as a preparation method and application of the catalyst. Belongs to the technical field of catalyst preparation. The catalyst is composed of a carrier, CuO and MOx, the CuO and the MOx are loaded on the carrier, Cu accounts for 10-50% of the total mass of the catalyst, M accounts for 1-25% of the total mass of the catalyst, M is one of Mn, Zn, Co, Ni, Fe, Cr, Ce, Nb, Ru, Pt, Ir and Pd, and the carrier is one of silicon oxide, aluminum oxide, magnesium oxide, lanthanum oxide, hydroxyapatite and magnesium-aluminum hydrotalcite. An oxide-oxide interface is formed between CuO and MOx through roasting and reduction, and relatively strong electron interaction exists between highly dispersed Cu nanoparticles and the oxide-oxide interface, so that the stability of the catalyst can be enhanced.

The invention discloses a high-entropy metal oxide catalyst as well as a preparation method and application thereof in CO catalytic oxidation, and belongs to the technical field of flue gas treatment. The preparation method comprises the following steps: dissolving copper salt, manganese salt, cerium salt, cobalt salt, vanadium salt and a dispersing agent into water to form a uniform solution, and slowly adding excessive alkali precipitant into the uniform solution to form a solid-liquid mixture; the solid-liquid mixture is transferred into a high-pressure kettle to be subjected to a hydrothermal reaction and then quenched, an obtained hydrothermal reaction product is calcined, and the high-entropy metal oxide catalyst is obtained and is high in catalytic oxidation activity on carbon monoxide at the low temperature, excellent in water resistance and sulfur resistance and particularly suitable for treatment of complex flue gas.

The invention discloses a preparation method and application of a high-entropy nano-enzyme with a multi-path synergistic antibacterial effect, and belongs to the field of nano-enzyme catalytic materials. According to the invention, the oxygen vacancy-rich high-entropy oxide with similar halogen peroxidase activity, similar peroxidase activity and similar glutathione oxide enzyme activity is synthesized by using a hydrothermal method and a high-temperature calcination method for the first time; bromide ions and hydrogen peroxide can be catalyzed to generate hypobromous acid with a bacterial quorum sensing interference effect and hydroxyl free radicals with a structural function destroying effect, glutathione with a bacterial internal redox balance maintaining effect is consumed, and multi-way synergistic efficient bacterial damage and inactivation are achieved. The problems that an existing antifouling nano-enzyme material is single in catalysis way and poor in component adjustability are solved, actual extension and application of the high-entropy nano-enzyme coating are achieved, and the high-entropy nano-enzyme coating has potential application prospects in the marine organism antifouling field.

The invention discloses an environment-friendly and efficient composite metal oxide catalyst, a preparation method thereof and application of the catalyst in flue gas denitration. According to the catalyst, TiO2 serves as a carrier, and metal oxides such as Mn, Fe, W and Mo and various auxiliaries are loaded. The preparation method comprises the steps of dissolving, mixing, precipitating and the like, and process parameters of each step are accurately controlled. The catalyst is activated at the temperature of 50 DEG C, the NO conversion rate at the temperature of 120 DEG C is 96.3% or above, and the catalyst keeps high activity in a wide temperature range of 100-400 DEG C, resists SO2 toxicity, is environmentally friendly and non-toxic, is suitable for flue gas denitration of industrial boilers and the like, and has remarkable advantages compared with the prior art.

The invention discloses a preparation method of CoWO (cobalt tungsten oxide) modified NbOp-n heterojunction NbO5 / CoWO photocatalyst powder. The preparation method comprises the following steps: dissolving cobalt salt and tungsten salt in deionized water, stirring and mixing, carrying out hydrothermal reaction in an autoclave, washing and drying to obtain CoWO powder; the preparation method comprises the following steps: dissolving niobium oxalate and ammonium carbonate in deionized water, adding CoWO powder, carrying out a hydrothermal reaction in an autoclave, and carrying out washing and drying treatment to prepare NbO / CoWO photocatalyst powder. According to the method, the hydrothermal reaction temperature is regulated and controlled, and the mass ratio of raw materials is optimized, so that the catalyst forms a p-n heterojunction structure of NbOmicron flower loaded CoWOnano particles. The prepared catalyst has high norfloxacin wastewater degradation efficiency under visible light irradiation, has the advantages of simple preparation process, low reagent cost, high catalytic activity and good structural stability, and can be effectively applied to purification treatment of antibiotic polluted water.

A method for producing hydrocarbons includes subjecting a first feed stream to steam cracking to obtain a first product stream, and subjecting an ethane-containing second feed stream to oxidative dehydrogenation to obtain a second product stream. A portion of the first product stream is subjected to a deethanization or a depropanization separately from the second product to obtain a lighter fraction and a heavier fraction. A demethanization feed stream is formed by combining at least a portion of the lighter fraction and at least a portion of the second product stream and is subjected at least in part to demethanization. Partial oxygen removal is carried out during the formation of the demethanization feed stream. The oxygen removal is carried out downstream of the combining step.

The invention relates to an oxide catalyst for high-activity and high-selectivity production of a target product pyromellitic dianhydride in the process of producing pyromellitic dianhydride through durene air selective oxidation. A multi-component efficient system is used for construction for preparation. The preparation method comprises the following steps: fully and uniformly mixing a certain amount of a main active component oxide and an auxiliary agent metal hydrochloric acid or an ionic liquid aqueous solution, carrying out a hydrothermal enhancement process to obtain catalyst active precursor slurry, adding a dilution auxiliary agent, and drying and roasting the slurry prepared in the previous step under certain conditions to obtain the efficient metal synergistic oxide catalyst. On the basis of coordinated benefit application of different components in a composite oxide material, the metal synergistic oxide is synthesized through hydrothermal heat assistance, the metal synergistic oxide has excellent catalytic performance in a reaction for producing pyromellitic dianhydride from durene, the yield of a target product is increased, and the metal synergistic oxide is suitable for industrial application.

The invention belongs to the technical field of catalytic materials and hydrocarbon reforming, and particularly relates to a high-entropy catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing a metal salt solution containing lanthanum, chromium, copper, zinc, manganese, nickel, iron and cobalt ions with a chelating agent and a dispersing agent for reaction, carrying out ultrasonic cavitation treatment to obtain sol, adjusting the pH value, gelatinizing under an oil bath heating condition to obtain a colloidal precursor, drying, and calcining in an air atmosphere to obtain a perovskite type high-entropy oxide precursor; and then treating in a reducing atmosphere to obtain the FeZnCuNiCo perovskite type high-entropy alloy catalyst which contains metal components of La, Cr, Ni, Mn, Fe, Zn, Cu and Co and takes a multi-metal alloy active center of Fe-Zn-Cu-Ni-Co as a main component. The high-entropy catalyst can meet the harsh requirements of high temperature, strong carbon deposition driving force and long-period operation in a propane dry reforming reaction, and is suitable for industrial application scenarios of continuous production of high-temperature synthesis gas.

The present invention relates to an ammonia decomposition catalyst and a manufacturing method thereof, and more particularly to an ammonia decomposition catalyst containing alumina (Al2O3), cerium (Ce), lanthanum (La), ruthenium (Ru) and potassium (K).

The present invention relates to the field of catalyst technology, discloses a supported noble metal catalyst and its preparation method and application, the catalyst includes a first carrier and a coating loaded on the first carrier, the raw material composition for preparing the coating includes a second carrier, an active component precursor, an auxiliary agent precursor, a binder and a dispersant; the first carrier is cordierite, mullite or cordierite-mullite; the second carrier is titanium dioxide and / or aluminum oxide; the active component precursor is selected from at least one of a platinum precursor, a palladium precursor and a rhodium precursor; the auxiliary agent precursor is a combination of a cerium precursor, a zirconium precursor and a neodymium precursor; the binder is a mixture of an organic binder, an inorganic binder and a coupling agent. The supported noble metal catalyst has low production cost, high catalytic activity, strong anti-poisoning ability and long service life, can be used for the removal of volatile organic compounds, and is particularly suitable for the removal of flue gases such as ethylene and propane with large air volume and low concentration of organic small molecule hydrocarbons.

The invention belongs to the field of carbon nanomaterials, and relates to a cobalt molybdenum / magnesium aluminum metal catalyst, a preparation method and application thereof, and a preparation method of a carbon nanotube. The preparation method of the cobalt molybdenum / magnesium aluminum metal catalyst comprises the following steps: S1, carrying out chelation reaction on metal salt and small molecular organic acid in a solvent, adjusting the pH value of the obtained chelation product to 3-7.5, and mixing the chelation product with a modifier to form gel; and S2, roasting the gel to obtain the cobalt molybdenum / magnesium aluminum metal catalyst. The preparation method is characterized in that in the preparation process of the cobalt-molybdenum / magnesium-aluminum metal catalyst, small-molecular organic acid is used as a chelating agent, and a specific modifier is used as an accelerant and a stabilizer, so that the prepared cobalt-molybdenum / magnesium-aluminum metal oxide has good structural stability and catalytic performance, and when the cobalt-molybdenum / magnesium-aluminum metal oxide is used as a carbon nanotube synthesis catalyst, the catalytic performance of the catalyst is greatly improved. Not only can the carbon yield be improved, but also the few-walled carbon nanotube with small tube diameter and high length-diameter ratio can be obtained.

The invention provides a composite carrier supported palladium catalyst for preparing succinic anhydride through maleic anhydride hydrogenation and a preparation method and application thereof.The structural general formula of the composite carrier supported palladium catalyst is Pd-A-X-Y / (Z1 + Z2), Z1 in a composite carrier is made of a high-specific-surface-area porous material, Z2 is made of a high-thermal-conductivity compact material, and X is larger than or equal to 1 and smaller than or equal to 2. The active component is composed of metal Pd and transition metal such as Ni or precious metal such as Ru, and the auxiliary agent is composed of oxides of alkali metal, alkaline earth metal or rare earth elements and oxides of high-valence elements such as Mo. The catalyst is prepared by an impregnation method, and the composite carrier supported palladium catalyst has excellent low-temperature activity, tolerance and stability in a reaction for preparing succinic anhydride by maleic anhydride hydrogenation, can bear high maleic anhydride concentration and high liquid hourly space velocity at low temperature, low pressure and low hydrogen-anhydride ratio, and simultaneously obtains high maleic anhydride conversion rate and succinic anhydride selectivity.

The invention discloses a Mo-Bi-based catalyst and a preparation method and application thereof.The catalyst comprises active components, the active components comprise spherical particles and molybdenum oxide nanorods attached to the surfaces of the spherical particles, and the spherical particles contain molybdenum and / or molybdenum oxide and bismuth and / or bismuth oxide. When the catalyst is applied to propylene oxidation synthesis of acrolein, the catalyst has the technical effect of high acrolein selectivity.

The invention relates to a preparation method and application of a composite piezoelectric catalytic material NaNbO3-coated BiFeO3 for rapidly degrading antibiotics, NaNbO3 is flaky crystal grains with [001] crystallographic orientation prepared by a two-step molten salt method, and BiFeO3 is micro-nano particles prepared by a coprecipitation method. Composite micro-nano BiFeO3 powder and [001] oriented NaNbO3 flaky grains form a heterojunction, conversion of mechanical energy and electric energy of the material is achieved under the ultrasonic vibration condition, inductive charges are generated on the surface of the material, and photon-generated carriers move reversely under driving of a built-in electric field. According to the invention, the piezoelectric catalytic degradation capability of the BiFeO3 and NaNbO3 composite piezoelectric catalytic materials with different proportions on four antibiotics, namely oxytetracycline, levofloxacin, carbamazepine and paracetamol in different time periods is researched. When the mass ratio of the BiFeO3 to the NaNbO3 composite material is 1: 3, the oxytetracycline degradation rate within 30 min can reach 78.2%, the oxytetracycline degradation rate within 120 min can reach 91.8%, and the piezoelectric electro-catalysis characteristic is rapid and efficient. The method disclosed by the invention has important significance in developing a high-efficiency piezoelectric catalyst for degrading antibiotics.