CN109939710B - Pd/MC redispersed by PdxSupported catalyst and preparation method and application thereof - Google Patents
Pd/MC redispersed by PdxSupported catalyst and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a Pd/MCx supported catalyst for Pd redispersion and a preparation method and application thereof. The preparation method of the Pd/MCx supported catalyst comprises the following steps: putting the Pd/MOx catalyst in a tubular furnace, calcining and carbonizing under the condition of introducing carbon-containing gas, and carbonizing metal oxide MOx in the Pd/MOx catalyst into metal carbide MCx to obtain the Pd/MCx supported catalyst; wherein, the metal M in the Pd/MOx catalyst is one or more of transition metals Mo, Fe, W, Ti, Co, Mn, Nb, V, Ta, Zr and Cr. The Pd/MCx catalyst prepared by the invention not only has high initial catalytic activity, but also can be regenerated in situ in a fixed bed reactor through oxidation-carbonization, so that the Pd particles in the Pd/MCx catalyst can be redispersed through reversible circulation, and the activity of the catalyst can be recovered; the catalyst of the invention has higher catalytic activity due to higher dispersion degree of Pd.
Description
Technical Field
The invention relates to Pd/MC redispersed by PdxA supported catalyst, a preparation method and application thereof.
Background
The supported palladium-based catalyst is a common hydrogenation catalyst and is widely applied to the fields of alkane hydrogenation, olefin hydrogenation, nitro and nitroso hydrogenation, catalytic selective oxidation and the like. For noble metal catalysts, the degree of dispersion of the noble metal is a very important indicator, directly determining the catalyst performance. But the catalyst is often used for a long time or at an excessively high temperature during the use process, so that sintering deactivation is caused, and the activity of the catalyst is reduced. In the case of sintered noble metal catalysts, in-situ regeneration is often lacking, and the most common method is to separate the noble metal from the noble metal catalyst and then prepare the catalyst again. Obviously, the process is not environment-friendly and has great economic cost, but the in-situ regeneration technology of the sintering catalyst has not been developed and applied in a breakthrough way.
Henrik Birgersson topic group by using cyclic O2,H2,Cl2Noble metals in the three-phase catalyst are redispersed in the atmosphere, and the commercial automobile three-phase catalyst is successfully regenerated. Polychronopoulo et al prepared and characterized with O2-Cl2Treatment of Pd/CeO2-Al2O3Reuse H2The reduction may effect the formation of small particle size Pd. Newton group of subjects successfully aged Pd/Al using a CO/NO atmosphere2O3The Pd particles in the catalyst redisperse and suggest possible mechanisms and processes for Pd particles.
Although the method can redisperse the noble metal catalyst, the method has a plurality of defects, such as low redispersion efficiency, environment-unfriendly atmosphere, ex-situ redispersion, undesirable activity recovery of the redispersed catalyst, and the like.
Disclosure of Invention
In order to solve the problem of sintering deactivation of the catalyst, the invention aims to provide a Pd/MCx supported catalyst redispersed by Pd, a preparation method and application thereof.
The preparation method of the Pd/MCx supported catalyst for redispersing Pd is characterized in that Pd/MO is addedxThe catalyst is placed in a tubular furnace and is calcined and carbonized under the condition of introducing carbon-containing gas, and the metal oxide MO in the Pd/MOx catalystxIs carbonized into metal carbide MCxObtaining the Pd/MCxA supported catalyst; wherein Pd/MOxThe metal M in the catalyst is one or more of transition metals Mo, Fe, W, Ti, Co, Mn, Nb, V, Ta, Zr and Cr; the Pd/MOxThe mass percentage of Pd in the catalyst is 0.05-10%, preferably 0.5-5%.
The Pd/MC redispersed by PdxThe preparation method of the supported catalyst is characterized in that the carbon-containing gas is alkane gas and H2The alkane gas is CH or CO4Or C2H6(ii) a Alkane gas and H2The volume concentration of the alkane gas in the mixed gas is 5-95%, preferably 10-20%.
The Pd/MC redispersed by PdxThe preparation method of the supported catalyst is characterized in that the calcination carbonization temperature is 300-700 ℃, and the calcination carbonization time is 0.5-12 h.
The Pd/MC redispersed by PdxThe preparation method of the supported catalyst is characterized by further comprising the following steps of: prepared Pd/MCxThe supported catalyst is also loaded with 0.05-5 wt% of metal auxiliary agent, and the metal auxiliary agent is at least one of Cu, K and Ba.
The Pd/MC redispersed by PdxA preparation method of a supported catalyst is characterized in that the Pd/MOxThe preparation process of the catalyst comprises the following steps: the MO is treated by an excess impregnation method or an equal volume impregnation methodxSoaking a carrier in a Pd precursor water solution, standing, drying and roasting, and then carrying out H treatment at the temperature of 200-300 DEG C2Reducing to make Pd in metallic state, i.e. obtaining Pd/MOxA catalyst; wherein the Pd precursor is one or more of chloropalladate, palladium acetate, palladium nitrate and palladium ammonia complex.
Pd redispersed Pd/MC prepared according to the above methodxA supported catalyst.
The Pd is redispersedPd/MC ofxUse of a supported catalyst, characterized in that the Pd/MC isxThe supported catalyst is used for catalyzing the hydrogenation and dechlorination reaction of halogenated hydrocarbon, the selective hydrogenation reaction of alkyne or the selective oxidation reaction of alcohol compounds.
The Pd redispersed Pd/MCxUse of a supported catalyst, characterized in that the Pd/MC isxAfter the sintering deactivation phenomenon of the supported catalyst occurs in the catalytic reaction, the catalyst is regenerated in situ by adopting the following process:
1) calcining the deactivated catalyst in oxygen-containing atmosphere for 0.5-12 hr to obtain metal carbide MC in the catalystxAnd the carbon deposit is converted into metal oxide MOxTo obtain Pd/MOxA catalyst;
2) Pd/MO obtained in the step 1)xThe catalyst is calcined and activated in a carbon-containing atmosphere, and Pd/MOxMetal oxide MO in catalystsxIs carbonized again into metal carbide MCxTo obtain Pd/MCxThe supported catalyst, i.e. the in situ regeneration process, is completed.
The Pd redispersed Pd/MCxThe application of the supported catalyst is characterized in that in the step 1), the gas in the oxygen-containing atmosphere is a mixed gas of oxygen and inert gas, the volume concentration of the oxygen is 5-95%, and the inert gas is nitrogen or argon; in the step 2), the gas of the carbon-containing atmosphere is alkane gas and H2The alkane gas is CH or CO4Or C2H6(ii) a Alkane gas and H2In the mixed gas of (1), H2The volume concentration is 5-95%.
The Pd redispersed Pd/MCxThe application of the supported catalyst is characterized in that in the step 1), the roasting temperature is 300-650 ℃, and preferably 400-500 ℃; in the step 2), the calcining and activating temperature is 300-700 ℃, and the calcining and activating time is 0.5-12 h.
Compared with the prior art, the invention has the following beneficial effects:
1. Pd/MC prepared by the inventionxThe catalyst not only has high initial catalytic activity, but also is sinteredThe catalyst can be regenerated in situ in a fixed bed reactor through oxidation-carbonization, so that Pd/MC can be realized through reversible circulationxThe Pd particles in the catalyst are redispersed, so that the activity of the catalyst is recovered;
2. when the catalyst is oxidized and carbonized for in-situ regeneration, the regeneration atmosphere is environment-friendly, and the activity of the catalyst is recovered to more than 90 percent of the initial activity;
3. Pd/MC of the inventionxThe preparation method of the supported catalyst is simple and the production cost is low;
4. the supported Pd/MC prepared by the inventionxThe catalyst is used in hydrodechlorination, selective hydrogenation, oxidation and other reactions, and has the advantages of good catalytic activity, excellent selectivity, high catalyst efficiency, long service life and the like.
Detailed Description
The present invention is further illustrated by the following examples, which should not be construed as limiting the scope of the invention.
Example 1
1g of fresh Pd/FeC with a Pd loading of 3%xThe catalyst is loaded into a fixed bed reactor, and is reduced for 2 hours at the temperature of 250 ℃ by introducing hydrogen. Then introducing CFC-115 gas at the reaction temperature of 300 ℃ and the space velocity of 720h-1The reaction is carried out under the condition that the feeding molar ratio of CFC-115 raw material to hydrogen is 1: 1.5. After 80h of reaction, when the conversion of CFC-115 was less than 65%, it was noted that the catalyst had been deactivated by sintering.
The sintering deactivated catalyst has oxygen content of 8%2/N2Roasting for 0.5h at the temperature of 450 ℃ in the atmosphere to obtain Pd/FeOxCatalyst, then 10% CH is introduced at 300 DEG C4/H2Mixed gas (i.e. CH)4/H2In the mixed gas, CH4The volume content of the catalyst is 10%) and calcining and carbonizing for 1h to recover Pd/FeCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same reaction conditions, the hydrodechlorination reaction of CFC-115 under the action of the regenerated catalyst is carried out again.
When the fresh catalyst and the regenerated catalyst in example 1 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
Example 2
1g of fresh Pd/FeC with a Pd loading of 9%xThe catalyst is loaded into a fixed bed reactor, and is reduced for 2 hours at the temperature of 250 ℃ by introducing hydrogen. Then introducing CFC-115 gas at the reaction temperature of 300 ℃ and the space velocity of 720h-1The reaction is carried out under the condition that the feeding molar ratio of CFC-115 raw material to hydrogen is 1: 1.5. After 80h of reaction, when the conversion of CFC-115 was less than 65%, it was noted that the catalyst had been deactivated by sintering.
The sintering deactivated catalyst has oxygen content of 16%2/N2Roasting for 8 hours at the temperature of 400 ℃ in the atmosphere to obtain Pd/FeOxCatalyst, then 20% CH is introduced at 650 DEG C4/H2Calcining and carbonizing mixed gas for 10 hours to recover Pd/FeCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same conditions, the hydrodechlorination of CFC-115 over the regenerated catalyst is carried out again.
When the fresh catalyst and the regenerated catalyst in the example 2 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
Example 3
1g of fresh Pd/FeC with a Pd loading of 5%xThe catalyst is loaded into a fixed bed reactor, and is reduced for 2 hours at the temperature of 250 ℃ by introducing hydrogen. Then introducing CFC-115 gas at the reaction temperature of 300 ℃ and the space velocity of 720h-1The reaction is carried out under the condition that the feeding molar ratio of CFC-115 raw material to hydrogen is 1: 1.5. After 80h of reaction, when the conversion of CFC-115 was less than 65%, it was noted that the catalyst had been deactivated by sintering.
The sintering deactivated catalyst has oxygen content of 6 percent2/N2Roasting for 1h at 500 ℃ in atmosphere to obtain Pd/FeOxIntroducing CO at the temperature of 300 ℃ to calcine and carbonize for 3 hours to recover Pd/FeCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same conditions, the hydrodechlorination of CFC-115 over the regenerated catalyst is carried out again.
When the fresh catalyst and the regenerated catalyst in the example 3 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
Example 4
1g of fresh Pd/FeC with a Pd loading of 10%xThe catalyst is loaded into a fixed bed reactor, and is reduced for 2 hours at the temperature of 250 ℃ by introducing hydrogen. Then introducing CFC-115 gas at the reaction temperature of 300 ℃ and the space velocity of 720h-1The reaction is carried out under the condition that the feeding molar ratio of CFC-115 raw material to hydrogen is 1: 1.5. After 80h of reaction, when the conversion of CFC-115 was less than 65%, it was noted that the catalyst had been deactivated by sintering.
The sintering deactivated catalyst has oxygen content of 12 percent2/N2Roasting for 6 hours at the temperature of 420 ℃ in the atmosphere to obtain Pd/FeOxThe catalyst is added with CO at the temperature of 650 ℃ to calcine and carbonize for 6 hours to recover Pd/FeCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same conditions, the hydrodechlorination of CFC-115 over the regenerated catalyst is carried out again.
When the fresh catalyst and the regenerated catalyst in the example 4 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
Example 5
Pd-Cu/MoO preparation by adopting continuous impregnation method3. Firstly, dropwise adding 2.51mL of copper nitrate aqueous solution with the Cu content of 0.4mol/L into 2g of MoO3Standing and soaking on a carrier, drying, and roasting at 300 deg.C in air atmosphere (the roasting is to increase copper precursor and MoO)3Interaction of the support) to obtain a calcined catalyst precursor; dropwise adding 3.85mL of palladium chloride aqueous solution containing 0.1mol/L of Pd on the calcined catalyst precursor, carrying out ultrasonic impregnation for 30min, standing, drying, and carrying out H treatment at the temperature of 250-300 DEG C2Reduction to obtain Pd-Cu/MoO3Catalyst, Pd-Cu/MoO3The catalyst is calcined and carbonized in a carbon-containing atmosphere to obtain the Pd-Cu/MoC catalyst.
1g of fresh catalyst (2% Pd-3% Cu/MoC catalyst, 3% Cu) was loaded in a fixed bed reactor, and reduced with hydrogen at 250 ℃ for 2 h. Then is introduced intoReaction raw material gas (raw material gas volume content composition: 1.09% C)2H2，1.85％H2，87.66％C2H4，9.40％N2The total flow is 200mL/min, the total pressure is 2.1 MPa), and acetylene selective hydrogenation reaction is carried out at the reaction temperature of 100 ℃. After a reaction time of 100h, C2H2When the conversion of (2) is less than 80%, sintering deactivation of the catalyst is regarded as occurring.
The sintering deactivated catalyst has oxygen content of 6 percent2/N2Roasting for 1h at 500 ℃ in the atmosphere to obtain Pd/MoOxCatalyst, then introducing 12% CH at 350 deg.C4/H2Calcining and carbonizing the mixed gas for 2 hours to recover Pd/MoCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same condition, the selective hydrogenation reaction of acetylene under the action of the regenerated catalyst is carried out again.
When the fresh catalyst and the regenerated catalyst in the example 5 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
Example 6
1g of fresh catalyst with the load of 8 percent Pd-10 percent Cu/MoC is loaded into a fixed bed reactor and is reduced for 2 hours at the temperature of 250 ℃ by introducing hydrogen. Then reaction raw material gas is introduced (the volume content of the raw material gas is 1.09 percent C)2H2，1.85％H2，87.66％C2H4，9.40％N2The total flow is 200mL/min, the total pressure is 2.1 MPa), and acetylene selective hydrogenation reaction is carried out at the reaction temperature of 100 ℃. After a reaction time of 100h, C2H2When the conversion of (2) is less than 80%, sintering deactivation of the catalyst is regarded as occurring.
The sintering deactivated catalyst has oxygen content of 16%2/N2Roasting for 8 hours at the temperature of 400 ℃ under the atmosphere to obtain Pd/MoOxCatalyst, then 20% CH is introduced at 600 DEG C4/H2Calcining and carbonizing the mixed gas for 10 hours to recover Pd/MoCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same condition, the selective hydrogenation reaction of acetylene under the action of the regenerated catalyst is carried out again.
When the fresh catalyst and the regenerated catalyst in example 6 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
Example 7
1g of fresh catalyst with the loading of 3 percent Pd-4 percent Cu/MoC is loaded into a fixed bed reactor, and hydrogen is introduced to reduce for 2 hours at the temperature of 250 ℃. Then reaction raw material gas is introduced (the volume content of the raw material gas is 1.09 percent C)2H2，1.85％H2，87.66％C2H4，9.40％N2The total flow is 200mL/min, the total pressure is 2.1 MPa), and acetylene selective hydrogenation reaction is carried out at the reaction temperature of 100 ℃. After a reaction time of 100h, C2H2When the conversion of (2) is less than 80%, sintering deactivation of the catalyst is regarded as occurring.
The sintering deactivated catalyst has oxygen content of 6 percent2/N2Roasting for 1h at 500 ℃ in the atmosphere to obtain Pd/MoOxIntroducing CO at 350 ℃ to calcine and carbonize for 3h to recover Pd/MoCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same condition, the selective hydrogenation reaction of acetylene under the action of the regenerated catalyst is carried out again.
When the fresh catalyst and the regenerated catalyst in example 7 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
Example 8
1g of fresh catalyst with the loading of 9 percent Pd-10 percent Cu/MoC is loaded into a fixed bed reactor, and hydrogen is introduced to reduce for 2 hours at the temperature of 250 ℃. Then reaction raw material gas is introduced (the volume content of the raw material gas is 1.09 percent C)2H2，1.85％H2，87.66％C2H4，9.40％N2The total flow is 200mL/min, the total pressure is 2.1 MPa), and acetylene selective hydrogenation reaction is carried out at the reaction temperature of 100 ℃. After a reaction time of 100h, C2H2When the conversion of (2) is less than 80%, sintering deactivation of the catalyst is regarded as occurring.
The sintering deactivated catalyst has oxygen content of 12 percent2/N2Atmosphere and 420 deg.CRoasting for 8 hours at the temperature to obtain Pd/MoOXIntroducing CO at the temperature of 600 ℃ to calcine and carbonize for 6 hours to recover Pd/MoCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same condition, the selective hydrogenation reaction of acetylene under the action of the regenerated catalyst is carried out again.
When the fresh catalyst and the regenerated catalyst in the example 8 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
Example 9
1g of fresh Pd/TiC catalyst with 2 percent of Pd loading capacity is loaded into a fixed bed reactor, and hydrogen is introduced to reduce for 2h at the temperature of 250 ℃. Then, the reaction feed gas was introduced (feed gas composition: 5 vol.% O)20.4 to 0.5 vol.% ethanol, N2For balancing gas, the total flow rate is 100mL/min, and the space velocity is 24000 h-1) The selective oxidation of ethanol to CO is carried out at a reaction temperature of 200 DEG C2The reaction of (1). After the reaction for 150h, when the conversion rate of the ethanol is less than 75%, the catalyst is marked as sintering deactivation.
The sintering deactivated catalyst has oxygen content of 8%2/N2Roasting for 0.5h at the temperature of 450 ℃ in the atmosphere to obtain Pd/TiOxCatalyst, then introducing 9% CH at 300 deg.C4/H2Calcining and carbonizing mixed gas for 1h to recover Pd/TiCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same conditions, the selective oxidation of the ethanol to CO is carried out again under the action of the regenerated catalyst2The reaction of (1).
When the fresh catalyst and the regenerated catalyst in the example 9 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
Example 10
1g of fresh Pd/TiC catalyst with the Pd loading of 8 percent is loaded into a fixed bed reactor, and hydrogen is introduced to reduce for 2h at the temperature of 250 ℃. Then, the reaction feed gas was introduced (feed gas composition: 5 vol.% O)20.4 to 0.5 vol.% ethanol, N2For balancing gas, the total flow rate is 100mL/min, and the space velocity is 24000 h-1) At a reaction temperature of 200 DEG CSelective oxidation of ethanol to CO2The reaction of (1). After the reaction for 150h, when the conversion rate of the ethanol is less than 75%, the catalyst is marked as sintering deactivation.
The sintering deactivated catalyst has oxygen content of 16%2/N2Roasting for 8 hours at the temperature of 400 ℃ in the atmosphere to obtain Pd/TiOxCatalyst, then introducing 18% CH at 650 deg.C4/H2Calcining and carbonizing mixed gas for 10 hours to recover Pd/TiCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same conditions, the selective oxidation of the ethanol to CO is carried out again under the action of the regenerated catalyst2The reaction of (1).
When the fresh catalyst and the regenerated catalyst in the example 10 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
Example 11
1g of fresh Pd/TiC catalyst with 4 percent of Pd loading is loaded into a fixed bed reactor, and hydrogen is introduced to reduce for 2h at the temperature of 250 ℃. Then, the reaction feed gas was introduced (feed gas composition: 5 vol.% O)20.4 to 0.5 vol.% ethanol, N2For balancing gas, the total flow rate is 100mL/min, and the space velocity is 24000 h-1) The selective oxidation of ethanol to CO is carried out at a reaction temperature of 200 DEG C2The reaction of (1). After the reaction for 150h, when the conversion rate of the ethanol is less than 75%, the catalyst is marked as sintering deactivation.
The sintering deactivated catalyst has oxygen content of 6 percent2/N2Roasting at 500 ℃ for 1h in atmosphere to obtain Pd/TiOxIntroducing CO at the temperature of 300 ℃ to calcine and carbonize for 3h to recover Pd/TiCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same conditions, the selective oxidation of the ethanol to CO is carried out again under the action of the regenerated catalyst2The reaction of (1).
When the fresh catalyst and the regenerated catalyst in the example 11 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
Example 12
1g of fresh Pd/TiC catalyst with a Pd loading of 10%Loading into a fixed bed reactor, and introducing hydrogen to reduce for 2h at 250 ℃. Then, the reaction feed gas was introduced (feed gas composition: 5 vol.% O)20.4 to 0.5 vol.% ethanol, N2For balancing gas, the total flow rate is 100mL/min, and the space velocity is 24000 h-1) The selective oxidation of ethanol to CO is carried out at a reaction temperature of 200 DEG C2The reaction of (1). After the reaction for 150h, when the conversion rate of the ethanol is less than 75%, the catalyst is marked as sintering deactivation.
The sintering deactivated catalyst has oxygen content of 12 percent2/N2Roasting for 6 hours at the temperature of 420 ℃ in the atmosphere to obtain Pd/TiOxIntroducing CO at 650 ℃ to calcine and carbonize for 8h to recover Pd/TiCxAnd (5) obtaining the regenerated catalyst by the activity of the catalyst. Under the same conditions, the selective oxidation of the ethanol to CO is carried out again under the action of the regenerated catalyst2The reaction of (1).
When the fresh catalyst and the regenerated catalyst in example 12 are used for catalytic reaction, a sample is taken for 20h of reaction, and the conversion rate and the selectivity of the reaction are detailed in table 1.
TABLE 1
As can be seen from Table 1, sintering deactivated Pd/MCxSupported catalysts on CO or CH4/H2Calcining and carbonizing in the atmosphere of mixed gas, and the catalytic activity of the obtained regenerated catalyst can be recovered to more than 90% of the initial activity of the fresh catalyst.
Whether Pd can be dispersed on the carrier depends on the strength of the interaction force between the carrier and the noble metal Pd. Generally, when there is a strong interaction force between Pd and the carrier, the dispersion degree of Pd is high and the stability is good (i.e. Pd with small particle size is not easy to migrate to form Pd with large particle size in chemical reaction or under high temperature condition, thereby avoiding deactivation). The noble metal Pd in the deactivated catalyst due to sintering, if redispersed as small Pd metal particles, depends on two conditions: pd compounds (e.g. PdC)x) Can be used forThe Pd compound is easier to spread on the surface of the carrier than Pd metal, and the interaction strength of the spread Pd compound and the carrier is stronger. If both conditions are satisfied, the large Pd particles can be re-dispersed into the small Pd particles. If only one or both of the conditions are satisfied, the re-dispersion phenomenon hardly occurs.
Pd/MOxThe catalyst is calcined and carbonized to obtain Pd/MCxThe supported catalyst enables the sintered Pd to be redispersible by the following mechanism: it is well known that one metal often spreads spontaneously over the surface of another metal to form an ultra-thin wetting layer. The noble-metal-like nature of the metal carbide ensures that the metal coating growing on the carbide can also spread on the surface of another metal to form an ultra-thin metal carbide layer, which is a prerequisite for redispersion of the metal carbide. Pd/MC deactivated by sinteringxCalcining the catalyst in an oxygen-containing atmosphere to form Pd/MOxAnd in the process of carbonizing under the proper operation condition in the carbon-containing atmosphere, the formed amorphous Pd metal carbide can exist in the form of an ultrathin wetting layer and spread on the surface spontaneously. This is because the interface charge transfer between the metal carbide support and the active component metal Pd enhances the strong interaction between the noble metal Pd and the metal carbide support to redisperse the noble metal Pd as electrons flow from the metal Pd to the metal carbide support.
The statements in this specification merely set forth a list of implementations of the inventive concept and the scope of the present invention should not be construed as limited to the particular forms set forth in the examples.
Claims (5)
1. The application of Pd/MCx supported catalyst for re-dispersing Pd is characterized in that Pd/MC is usedxThe supported catalyst is used for catalyzing the hydrodechlorination reaction of halogenated hydrocarbon, the selective hydrogenation reaction of alkyne or the selective oxidation reaction of alcohol compounds;
Pd/MCxafter the sintering deactivation phenomenon of the supported catalyst occurs in the catalytic reaction, the catalyst is regenerated in situ by adopting the following process:
1) deactivating sinteringThe catalyst is roasted for 0.5 to 12 hours in oxygen-containing atmosphere, and the metal carbide MC in the catalystxAnd the carbon deposit is converted into metal oxide MOxTo obtain Pd/MOxA catalyst;
2) Pd/MO obtained in the step 1)xThe catalyst is calcined and activated in a carbon-containing atmosphere, and Pd/MOxMetal oxide MO in catalystsxIs carbonized again into metal carbide MCxTo obtain Pd/MCxThe supported catalyst, namely the in-situ regeneration process is completed;
in the step 1), the gas in the oxygen-containing atmosphere is a mixed gas of oxygen and inert gas, the volume concentration of the oxygen is 5-95%, and the inert gas is nitrogen or argon; in the step 2), the gas of the carbon-containing atmosphere is alkane gas and H2The alkane gas is CH or CO4Or C2H6(ii) a Alkane gas and H2In the mixed gas of (1), H2The volume concentration is 5-95%;
in the step 1), the roasting temperature is 400-500 ℃; in the step 2), the calcining and activating temperature is 300-700 ℃, and the calcining and activating time is 0.5-12 h;
the preparation method of the Pd redispersed Pd/MCx supported catalyst comprises the following steps: Pd/MOxThe catalyst is placed in a tubular furnace and is calcined and carbonized under the condition of introducing carbon-containing gas, and the metal oxide MO in the Pd/MOx catalystxIs carbonized into metal carbide MCxObtaining the Pd/MCxA supported catalyst; wherein Pd/MOxThe metal M in the catalyst is one or more of transition metals Mo, Fe, W, Ti, Co, Mn, Nb, V, Ta, Zr and Cr; the Pd/MOxThe mass percentage of Pd in the catalyst is 0.5-5%.
2. The use of a Pd redispersed Pd/MCx supported catalyst as claimed in claim 1, wherein the Pd redispersed Pd/MCx supported catalyst is prepared by a process comprising the carbon-containing gas being an alkane gas and H2Mixed gas or CO, the alkane gas being CH4Or C2H6Alkane gas and H2OfIn the synthesis gas, the volume concentration of alkane gas is 10-20%.
3. The use of the Pd redispersed Pd/MCx supported catalyst as claimed in claim 1, wherein the Pd redispersed Pd/MCx supported catalyst is prepared by calcining and carbonizing at 300-700 deg.C for 0.5-12 h.
4. The use of a Pd-redispersed Pd/MCx supported catalyst as claimed in claim 1, wherein the Pd-redispersed Pd/MCx supported catalyst is prepared by a process further comprising the steps of: prepared Pd/MCxThe supported catalyst is also loaded with 0.05-5 wt% of metal auxiliary agent, and the metal auxiliary agent is at least one of Cu, K and Ba.
5. The use of a Pd redispersed Pd/MCx supported catalyst as claimed in claim 1, wherein the Pd/MO is present in the form of a supported catalystxThe preparation process of the catalyst comprises the following steps: the MO is treated by an excess impregnation method or an equal volume impregnation methodxSoaking a carrier in a Pd precursor water solution, standing, drying and roasting, and then carrying out H treatment at the temperature of 200-300 DEG C2Reducing to make Pd in metallic state, i.e. obtaining Pd/MOxA catalyst; wherein the Pd precursor is one or more of chloropalladate, palladium acetate, palladium nitrate and palladium ammonia complex.
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