JP5736624B2 - CO shift catalyst - Google Patents

Description

The present invention relates to a CO shift catalyst for converting CO present in synthesis gas or the like into CO ₂ .

In industrial operation, the water gas shift reaction is used to convert CO to CO ₂ which is represented by Formula 1 below.

CO + H ₂ O → CO ₂ + H ₂ H = −9.84 Kcal / mol at 298 ° K (Formula 1)

  As a CO shift catalyst, Patent Document 1 discloses that a catalyst powder prepared by a coprecipitation method from a nitrate solution of Cu and Zn is formed into pellets, impregnated in a Teflon (registered trademark) dispersion, dried, and then Teflon (registered). (Trademark) is attached to the pellet surface, and a method for preparing a shift catalyst and a prepared catalyst are disclosed.

Patent Document 2 includes about 5 to about 70% by weight copper oxide, about 20 to about 50% zinc oxide, about 5 to about 50% by weight aluminum oxide, and has a copper surface area of at least about 22 m ² / A low temperature water gas shift catalyst characterized by g is disclosed.

  In the invention according to the above disclosure, the catalyst itself is in the form of a powder, has poor heat resistance, and the use site is limited. For example, in the reaction chamber in which the methanol reforming catalyst is disposed, the exposed temperature is too high, so that it cannot coexist with the reforming catalyst. In addition, when the reformed gas is transported from the reaction section equipped with the reforming catalyst, the shift catalyst is arranged in the transport pipe, and if the CO can be removed, the system becomes compact. Even if the wash coat can be carried out, there is a high possibility of clogging, and there is a problem that a reaction part for installing the shift catalyst must be provided separately from the reforming catalyst reaction part.

JP 2004-089813 A JP 2005-52089A

  An object of the present invention is to provide a CO shift catalyst that can be used as an alloy-based catalyst at a site that cannot be used with a conventional powdery CO shift catalyst.

  The CO shift catalyst of the present invention made to solve the above-mentioned problems is characterized by using a plate-like alloy on which nano / micro protrusions made of Cu-Zn are grown and formed.

  In the above-described invention, the nano / micro protrusions made of Cu-Zn have a conical shape, a round cross section including a circular column or a truncated pyramid, and a ratio of the length to the bottom outer diameter of 3 μm or less. The aspect ratio is 5 or more.

  Delete

Conventional catalysts are Cu-ZnO-based or Cu-ZnO-Al ₂ O ₃ system centered, one Re powdery catalyst in the case of molding into pellets, or wash-coated on a substrate such as cordierite honeycomb It is used. However, since the heat resistance of Cu—ZnO itself is not necessarily high, its use site has been limited. In the present invention, by generating active species on the surface of the plate-like alloy by Ar ion irradiation treatment, a CO shift catalyst having excellent heat resistance and a wide shape of use compared to conventional powder catalysts is produced. I was able to. As an example of application, by lining a catalyst using this plate-like alloy on the inner wall of a fuel reforming vessel that requires high temperature, it is possible to cause a CO shift reaction immediately from the synthesis gas produced by the reforming catalyst. Thus, the system can be miniaturized.

It is a SEM photograph which shows the surface of an Ar ion beam non-processed goods. It is a SEM photograph which shows the nano * micro processus | protrusion formed in the surface of the Ar ion beam 10 minute processed goods. It is a SEM photograph which shows the nano-micro processus | protrusion formed in the surface of the Ar ion beam 30 minute processed goods. It is a SEM photograph which shows the nano-micro processus | protrusion formed in the surface of the Ar ion beam 70 minute processed goods. It is a graph which shows the change of the volume of a nano-micro processus by irradiation time. It is a graph which shows a Johnson-Mehl-Avrami plot. It is a SEM photograph which shows the nano * micro processus | protrusion formed in the surface of the Ar ion beam 20 minute processed goods. It is a SEM photograph which shows the nano * micro processus | protrusion formed in the surface of the Ar ion beam 40 minute processed goods. It is a conceptual diagram which shows the reaction container and the filling state of a sample. It is a schematic block diagram of a reactor. It is a graph which compares and shows the conversion rate of each process goods.

  Hereinafter, embodiments of the present invention will be described in detail.

  First, a method for forming nano / micro protrusions on the surface of a plate-like alloy will be described.

  In the present invention, the surface of the plate-like Cu—Zn alloy is irradiated with an Ar ion beam under a low vacuum to form nano / micro protrusions. First, an alloy plate made of a Cu—Zn alloy is prepared. As the alloy plate, a brass plate of Cu65% Zn35% can be used. In the present invention, 7: 3 brass or 6: 4 brass can be used as the alloy plate, and a Cu—Zn alloy having a Zn concentration of 20 to 80% can be used. Further, cast material, hot forged material, and hot rolled material may be used as the alloy plate, but a material that has undergone cold working such as cold rolling and self-assembled to accumulate plastic strain is used. Is desirable. This is because nano / micro protrusions can be rapidly grown by releasing the plastic strain. The alloy plate is pickled with diluted hydrochloric acid or the like to activate the surface.

Next, protrusions are grown by surface diffusion of Cu atoms and Zn atoms excited by irradiating the alloy plate with an Ar ion beam under vacuum. The degree of vacuum is a so-called low vacuum of about 10 ⁻² to 10 ⁻³ Pa. This is because if the degree of vacuum is lower than 10 ⁻² Pa, the oxidation of Zn proceeds to become ZnO, and if the degree of vacuum is higher than 10 ⁻³ Pa, irradiation with an Ar ion beam becomes difficult.

  Furthermore, it is desirable that the irradiation angle of the Ar ion beam is 20 to 90 ° with respect to the plate surface, and the acceleration voltage is 2 to 20 kV. If the irradiation angle is less than 20 °, it is difficult to efficiently supply the energy of the Ar ion beam, and desirable nano- and micro-projections such as conical shapes are not formed. This is because there is no need to perform irradiation. Further, the acceleration voltage is set to 2 to 20 kV when the Ar ion beam which is a high energy beam is irradiated, the irradiation voltage such as a point defect or a low voltage of 20 kV or less in which implanted ions are not easily introduced. On the other hand, if it is less than 2 kV, the voltage is too weak. When a Penning ion source is used, it is desirable that the acceleration voltage is 5 to 10 kV, the irradiation angle is 20 to 90 °, and the irradiation time is 10 to 90 minutes. The current of the Ar ion beam is preferably 0.5 to 1.5 mA.

  In addition, the beam irradiated in the present invention is not limited to the Ar ion beam, but may be any high energy beam capable of growing nano / micro protrusions. In addition to the Ar ion beam, an electron beam, a laser beam, X-rays, γ-rays, neutron beams, particle beams and the like can be used.

  A preferred nano / micro-projection shape is generally conical and round in cross section, but may include a cylinder. Further, it may have a truncated pyramid shape. The nano / micro protrusions preferably have an aspect ratio (= h / d) of 5 or more, which is the ratio of the protrusion height h to the diameter d of 3 μm or less on the bottom surface. The reason why the aspect ratio is 5 or more is that if it is less than 5, sufficient effects cannot be exhibited in the electron emission characteristics and the like. On the other hand, the upper limit of the aspect ratio is not set because there is no problem in using the aspect ratio no matter how large.

A substrate having a width of 2 mm, a length of 10 mm and a thickness of 0.2 mm was cut out from a cold-rolled brass plate to prepare a substrate. The brass plate is composed of an α phase having an fcc structure and a β ′ phase having a CsCl type. The substrate was pickled with 1.6 molar aqueous hydrochloric acid and then heated to 150 ° C. in the atmosphere. Immediately after that, it was inserted into a vacuum chamber, kept at a vacuum degree of 10 ⁻³ Pa, and irradiated with an Ar ion beam at an irradiation angle of 40 °, an acceleration voltage of 5 kV or 9 kV, and a current of 0.5 mA for 10 to 70 minutes. After irradiation, the nano / micro protrusions on the irradiated surface and the shape of the substrate were observed with a scanning electron microscope and Laser Scanning Microscopy (LSM), and the composition and phase were analyzed with EPMA and Glancing Angle X-ray Diffraction (GAXRD).

  Scanning electron micrographs of the surface of the brass plate at an acceleration voltage of 9 kV and irradiation times of 0 minutes, 10 minutes, 30 minutes, and 70 minutes are shown in FIGS. Of course, in the non-processed product, the protrusion does not grow. Recrystallization occurred after irradiation for 10 minutes, and bumps appeared on the surface. Thereafter, it is recognized that conical nano / micro protrusions grow as the irradiation time becomes longer, 30 minutes and 70 minutes.

  As shown in FIG. 5, for the conical nano / micro protrusion, the volume of the protrusion was determined from the diameter X, height h, or h ′ of the bottom surface of the nano / micro protrusion. FIG. 5A shows the relationship between the irradiation time and the protrusion volume at an acceleration voltage of 5 kV, and FIG. 5B shows the relationship between the irradiation time and the protrusion volume. In either case, the volume increases with time. After that, it was saturated for some time.

Next, the growth mechanism of conical projections was estimated by the Johnson-Mehl-Avrami equation. The Johnson-Mehl-Avrami equation is the following Equations 2 and 3.
X = 1−exp (−Btk) (Formula 2)
lnln {1 / (1-X)} = klnt + lnB (Formula 3)

  In the above formulas 2 and 3, X is a volume fraction, T is time, and k is an Avrami index. Therefore, the growth mechanism can be estimated by obtaining k from the relationship between klnt and lnln {1 / (1-X)}.

  FIG. 6A is a graph showing the above relationship at an acceleration voltage of 5 kV, and k was about 2.27. FIG. 6B is a graph showing the above relationship at an acceleration voltage of 9 kV, and k was about 1.81. Since the values of k are different from each other, the growth of nano / micro protrusions is diffusion-controlled, but the growth rate may be different depending on the acceleration voltage. For example, when k = 1.5 to 2.5, it is considered that the nucleation point grows at a diffusion-controlled rate while decreasing.

  In the EPMA analysis, it was recognized that Zn was concentrated on the nano / micro protrusions. Further, it was confirmed that there are two regions in the Zn concentration band, that is, a Zn35-40 mass% α phase and a Zn45 mass% β ′ phase. In addition, it was found that the Zn concentration tends to increase with increasing irradiation time in the base portion at the acceleration voltage of 9 kV.

  FIGS. 7 and 8 show scanning electron micrographs of processed products with an acceleration voltage of 9 kV, an irradiation time of 20 minutes, and a treatment time of 40 minutes. The product shown in FIG. 7 is a 20-minute treated product, which is a nano / micro protrusion containing a small amount of Zn but mainly made of Cu. The bottom surface has a diameter of 0.5 to 1 μm and an aspect ratio of 10 to 20. It was. In addition, what is shown in FIG. 8 is a 40-minute processed product, and in addition to a large number of minute nano / micro protrusions of about 1 μm, nano / micro protrusions made of relatively large Cu—Zn are scattered. The aspect ratio of the minute nano / micro protrusions was about 10.

  Using the 20-minute treated product and the 40-minute treated product as described above together with the untreated product, the CO conversion rate in the CO shift reaction was measured. As a comparative material, an untreated product not irradiated with an Ar ion beam was used.

  FIG. 9 shows the filled state of the reaction vessel and the sample. The reaction vessel is made of SUS316, has an opening at the top, has a height in the vessel of 10 mm, and an inner diameter of 25 mm. Nine untreated products, 20-minute treated products, and 40-minute treated products were arranged in a cross shape as shown in the figure inside the reaction vessel.

  FIG. 10 shows a schematic configuration of the reaction apparatus. That is, a reaction vessel filled with nine samples is inserted between the upper and lower heaters for catalyst heating and heated, and a reaction gas containing CO is inserted into the heater and introduced into the reaction vessel. Was introduced into a quadrupole mass spectrometer to measure the CO conversion. The gas composition before the reaction was CO (1%) + H 2 O (5%) + He (remainder), the gas flow rate was 40 ml / min, and the reaction temperature was 400 ° C.

  As a result of the measurement, the CO conversion rate of the untreated product was 2.2%, but the CO conversion rate of the 20-minute treated product was 15.4%, and the CO conversion rate of the 40-minute treated product was 13.5%. Thus, it was found that the CO conversion rate of the treated product was increased by about 7 times that of the untreated product (FIG. 11). Therefore, it was confirmed that the present invention has a great industrial value as a plate-like CO shift catalyst having a high CO conversion rate that can be used in a site where the conventional powder catalyst cannot be used.

Further, when the CO conversion rate was measured in the same manner as described above for an alloy plate in which a brass plate was irradiated with an Ar ion beam at an acceleration voltage of 5 kV for 40 minutes to form nano / micro protrusions, the CO conversion rate was 8%. I confirmed that there was.

Claims (2)

  A CO shift catalyst characterized by using a plate-like alloy on which nano / micro protrusions made of Cu-Zn are grown and formed. The nano / micro protrusions made of Cu-Zn have a circular or truncated pyramid shape including a cone and a cylinder, and an aspect ratio that is a ratio of a length to a bottom outer diameter of 3 μm or less is 5 or more. The CO shift catalyst according to claim 1, wherein