US-20260124581-A1 - Exhaust Gas Purifying Catalyst and Catalyst Body using the Same

US20260124581A1US 20260124581 A1US20260124581 A1US 20260124581A1US-20260124581-A1

Abstract

An exhaust gas purifying catalyst whose oxidation activity after long exposure to high temperature is improved is provided. The exhaust gas purifying catalyst disclosed herein includes a parent material including an alumina particle and zirconia that covers at least a part of a surface of the alumina particle, and a catalyst precious metal carried by the parent material and containing at least Pt. The average particle diameter of the zirconia that is obtained by a focused ion beam scanning electron microscope is 50 nm or less. The mole ratio (ZrO 2 /Pt) of the zirconia to the Pt is 8 or more.

Inventors

Eriko Tanaka
Toshiki Tani
Shunsuke OISHI
Hiromi Togashi
Masanao Sato

Assignees

CATALER CORPORATION

Dates

Publication Date: 20260507
Application Date: 20230824
Priority Date: 20221018

Claims (14)

1 . An exhaust gas purifying catalyst comprising: a parent material including an alumina particle and zirconia that covers at least a part of a surface of the alumina particle; and a catalyst precious metal carried by the parent material and containing at least Pt, wherein an average particle diameter of the zirconia that is obtained by a focused ion beam scanning electron microscope is 50 nm or less, and a mole ratio (ZrO 2 /Pt) of the zirconia to the Pt is 8 or more.
2 . The exhaust gas purifying catalyst according to claim 1 , wherein when quantitative line analysis of Zr is performed using a field emission electron probe micro-analyzer from the surface of the alumina particle toward a center and a depth from the surface to the center is expressed with the surface defined as 0% and the center defined as 100%, a peak top of Zr intensity is within a range of 0 to 30%.
3 . The exhaust gas purifying catalyst according to claim 1 , wherein a mass ratio of the zirconia in the parent material is 5 mass % or more and 30 mass % or less.
4 . The exhaust gas purifying catalyst according to claim 1 , wherein the mole ratio (ZrO 2 /Pt) is 30 or less.
5 . The exhaust gas purifying catalyst according to claim 1 , wherein the catalyst precious metal does not contain Rh.
6 . An apparatus comprising a base material and a catalyst layer provided on the base material, wherein the catalyst layer contains the exhaust gas purifying catalyst according to claim 1 .
7 . The apparatus according to claim 6 , wherein the catalyst layer includes a lower layer part existing on a side of the base material, and an upper layer part existing on a side of a surface of the catalyst layer, the lower layer part of the catalyst layer contains the exhaust gas purifying catalyst, and the upper layer part contains an exhaust gas purifying catalyst different from the exhaust gas purifying catalyst in the lower layer part.
8 . The apparatus according to claim 6 , wherein the catalyst layer includes a former stage part existing on an upstream side of the catalyst layer and a latter stage part existing on a downstream side of the catalyst layer in a flowing direction of exhaust gas, the latter stage part of the catalyst layer contains the exhaust gas purifying catalyst, and the former stage part contains an exhaust gas purifying catalyst different from the exhaust gas purifying catalyst in the latter stage part.
9 . The exhaust gas purifying catalyst according to claim 2 , wherein a mass ratio of the zirconia in the parent material is 5 mass % or more and 30 mass % or less.
10 . The exhaust gas purifying catalyst according to claim 2 , wherein the mole ratio (ZrO 2 /Pt) is 30 or less.
11 . The exhaust gas purifying catalyst according to claim 2 , wherein the catalyst precious metal does not contain Rh.
12 . An apparatus comprising a base material and a catalyst layer provided on the base material, wherein the catalyst layer contains the exhaust gas purifying catalyst according to claim 2 .
13 . The apparatus according to claim 12 , wherein the catalyst layer includes a lower layer part existing on a side of the base material, and an upper layer part existing on a side of a surface of the catalyst layer, the lower layer part of the catalyst layer contains the exhaust gas purifying catalyst, and the upper layer part contains an exhaust gas purifying catalyst different from the exhaust gas purifying catalyst in the lower layer part.
14 . The exhaust gas purifying catalyst body according to claim 12 , wherein the catalyst layer includes a former stage part existing on an upstream side of the catalyst layer and a latter stage part existing on a downstream side of the catalyst layer in a flowing direction of exhaust gas, the latter stage part of the catalyst layer contains the exhaust gas purifying catalyst, and the former stage part contains an exhaust gas purifying catalyst different from the exhaust gas purifying catalyst in the latter stage part.

Description

TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst, and an exhaust gas purifying catalyst body using the same. The present application claims priority based on Japanese Patent Application No. 2022-166917 filed on Oct. 18, 2022, the entire contents of which application are incorporated herein by reference. BACKGROUND ART The exhaust gas emitted from an internal-combustion engine such as a vehicle engine includes toxic substances such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx). For efficient reaction and removal of these toxic substances from the exhaust gas, exhaust gas purifying catalysts have been used generally. In these exhaust gas purifying catalysts, a catalyst precious metal is carried in a parent material such as alumina (see Patent Literatures 1 and 2). For example, Patent Literature 1 describes an exhaust gas purifying catalyst in which zirconia and platinum (Pt) are carried in an alumina particle. According to Patent Literature 1, zirconia plays a role of a blocking material for suppressing the particle growth of Pt in the exhaust gas purifying catalyst described above; therefore, sintering of Pt is suppressed even after long exposure to the exhaust gas with high temperature and in particular, the decrease in oxidation activity to oxidize nitrogen monoxide (NO) can be suppressed. CITATION LIST Patent Literatures [Patent Literature 1] Japanese Patent Application Publication No. 2013-198879[Patent Literature 2] Japanese Patent Application Publication No. 2006-198594 SUMMARY OF INVENTION In Example according to Patent Literature 1, the durability is evaluated with the oxidation activity after a thermal process at 800° C. for 20 hours. However, considering the durability for a longer time, there is still room for improvement in the conventional art. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an exhaust gas purifying catalyst in which oxidation activity after long exposure to high temperature is improved. The present inventors have considered to suppress the decrease in oxidation activity of a catalyst precious metal in a way different from Patent Literature 1. That is to say, the present inventors' earnest examination indicates that the catalyst precious metal tends to become an oxidized state with low activity in a lean atmosphere. On the other hand, the acid property of a carrier that carries the catalyst precious metal has an influence on an electron state of the catalyst precious metal. Therefore, the present inventors have considered that the catalyst precious metal can be kept in an electron-rich state (metal state) with the high activity when the acid property of alumina is changed to increase the number of acid sites, and thus the decrease in oxidation activity of the catalyst precious metal can be suppressed even after the endurance. One method to increase the number of acid sites of alumina is to add zirconia. However, since the acid site is estimated to be generated at an interface between alumina and zirconia, it is necessary that miniaturized zirconia be disposed on a surface of alumina. However, as illustrated in FIG. 12, in a conventional exhaust gas purifying catalyst 100X as described in Patent Literatures 1 and 2, zirconia 34X disposed on a surface of alumina 32X has an average particle diameter (secondary particle diameter) of about 100 nm or more and for example 100 to 1000 nm due to, for example, a manufacturing method. In this manner, in the conventional art, the particle diameter of the zirconia 34X is large and the number of interfaces between alumina and zirconia is small; therefore, according to the present inventors' investigation, the effect of increasing the number of acid sites of the alumina 32X is not obtained. Based on such knowledge, the present inventors have considered that when the average particle diameter of the zirconia 34X is made smaller than before to increase the number of contact points between the alumina 32X and the zirconia 34X, the number of acid sites of alumina 32X is increased and in this case, a catalyst precious metal 40X can be easily kept in the metal state and in the end, the decrease in oxidation activity can be suppressed at a higher level. The present invention has been created accordingly. The present invention provides an exhaust gas purifying catalyst [1] including: a parent material including an alumina particle and zirconia that covers at least a part of a surface of the alumina particle; and a catalyst precious metal carried by the parent material and containing at least Pt, in which an average particle diameter of the zirconia that is obtained by a focused ion beam scanning electron microscope is 50 nm or less, and a mole ratio (ZrO3/Pt) of the zirconia to the Pt is 8 or more. In the exhaust gas purifying catalyst [1], zirconia that is miniaturized more than before is contained by a predetermined