Nghiên cứu tạo lớp mạ tổ hợp ni ceo2 cuo định hướng ứng dụng làm chất xúc tác cho quá trình oxy hóa khí thải từ động cơ đốt trong tt tiếng anh

Main tasks of the thesis: - Investigating the effect of CuO and CeO2 particles on the discharge of Ni2+ ions in nickel sulphate solution by cathodic potentiodynamic and electrochemical

MINISTRY OF EDUCATION

AND TRAINING

MINISTRY OF NATIONAL

DEFENCE

ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY

MAI VAN PHUOC

RESEARCH ON CREATING Ni-CeO2-CuO COMPOSITE PLATING ORIENTED TO APPLICATION AS A CATALYST FOR OXIDATION

OF EMISSIONS FROM INTERNAL COMBUSTION ENGINES

Specialized: Chemical Engineering Code: 9 52 03 01

SUMMARY OF ENGINEERING DOCTORAL THESIS

Hanoi - 2019

ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY

Scientific supervisor:

1 Prof.Dr.Sci Nguyen Duc Hung

Reviewer 1: Prof.Dr Mai Thanh Tung

Reviewer 2: Assoc Prof Dr Vu Thi Thu Ha

Reviewer 3: Assoc Prof Dr Nguyen Duy Ket

The defense of this dissertation will be held at the Academy of Military

Science and Technology Council,

at …… in 2019

Contacting with the dissertation by:

- Library of Academy of Military Science and Technology

- National Library of Vietnam

INTRODUCTION

1 The necessity of the thesis:

Toxic substances such as carbon monoxide, hydrocarbons, solid particles and NOx are usually emitted when gas and oil fuel being used These are substances that greatly affect human health and the environment, as creating acid rain, photochemical blindness, affecting the ozone layer, leading to climate change and the increase

of types of lung and cardiovascular diseases, especially cancers Therefore, it is necessary to remove these toxic substances from the exhaust air stream before discharging into the environment Improvements in the structure and operation mode of the engine cannot meet the requirements and standards of emissions Therefore, catalytic processor is the most effective tool to treat emissions to achieve environmental standards

Catalytic activity phases usually are precious metals such as platin (Pt), rhodium (Rh), palladium (Pd) Recently, many studies have shown that the catalytic activity of CeO2-based systems for oxidation is significantly improved by doping not only precious metals but also transition metals Therefore, the discovery of catalysts based on low-cost but highly catalytic transition metals has attracted the attention of scientists Among them, the mixture of CuO and CeO2 is a catalyst with many preeminent properties to minimize the pollution of engine exhaust The catalytic activity of these two oxide mixtures for oxidation reactions is comparable to catalysts based on precious metals

CeO2-CuO catalytic system can be made by various methods such as co-precipitation, sol-gel, combustion, thermal decomposition, precipitation - decomposition, chelation, impregnation, hydrothermal, chemical plating, mechanical mixing metal oxides together, By using these fabrication methods, to disperse the CeO2-CuO catalyst on the catalyst carrier must first create a carrier layer (commonly known as cordierite 2MgO.2Al2O3.5SiO2, γ-Al2O3), then the catalyst layer disperses and adheres to monolithe substrate (monolithe ceramic or metal monolithe)

CeO2-CuO catalyst can be created directly on the surface of steel plate by making Ni-CeO2-CuO electroplating from CeO2 and CuO nano catalytic particles In particular, Ni acts as a binder, disperses and binds CuO and CeO2 particles directly to the carrier without creating intermediate substrate as other methods

The above are the bases for PhD student to select and propose the

thesis topic "Research on creating Ni-CeO 2 -CuO composite plating oriented to application as a catalyst for oxidation of emissions from internal combustion engines"

2 Objectives of the thesis:

- Creating Ni-CeO2-CuO composite coatings on 430 stainless steel

- Finding the optimal conditions to creat Ni-CeO2-CuO composite plating (direct current plating technique, pulse current plating technique: current density, solid particle concentration, stirring speed, plating time, )

- Determining the catalytic activity for oxidation of CO, hydrocarbons of the emissions from internal combustion engine of CeO2-CuO mixture on Ni-CeO2-CuO composite plating

3 Main tasks of the thesis:

- Investigating the effect of CuO and CeO2 particles on the discharge of Ni2+ ions in nickel sulphate solution by cathodic potentiodynamic and electrochemical impedance spectroscopy

- Surveying the technological parameters of direct current plating technique affecting the content of CeO2 and CuO particles on the platings

- Investigating the technological parameters of pulse current plating technique affecting the content of CeO2 and CuO particles on the platings

- Researching mechanical properties of Ni-CeO2-CuO composite platings: corrosion resistance, abrasion resistance, thermal shock stability, micro hardness

- Evaluating the catalytic activity for oxidation of CO, hydrocarbons of the emissions from internal combustion engine of CeO2-CuO mixture on the Ni-CeO2-CuO composite plating.

4 Research methodogoly of the thesis:

- The effects of CuO and CeO2 particles on the discharge of Ni2+

ions in plating process was identified by cathodic potentiodynamic measurements and electrochemical impedance spectroscopies

- The content of CuO and CeO2 particles on the surface of CeO2-CuO composite platings was determined by energy dispersive analyzer spectrum (EDX)

Ni The distribution of CuO and CeO particles on the platings was

determined by scanning electron microscopy method (SEM) and element mapping

- The catalytic activity of the composite platings was found out by

micro current-reaction method

5 The significance of the thesis:

- Scientific significance: results of the thesis generate scientific

basis for electrochemical technology to make catalytic metal-CuO, CeO2 nanocomposite coating

- Practical significance: contribute to the establishment of plating

technology process of producing catalytic plating applied in the field

of engine exhaust treatment

6 The layout of the thesis :

The 149-page thesis include: Introduction (4 pages); Chapter 1 Overview (39 pages); Chapter 2 Experimental and Research Methods (13 pages); Chapter 3 Results and discussion (73 pages); Conclusions (2 pages); 146 references

- Catalytic properties of CeO2 and CuO mixture and methods for preparing them

- Electrodes: Ni, Cu, Ti mesh coated RuO2

Cathode material is 430 stainless steel sheet with thickness of 0.2

mm

2.2 Experiments

- Research solution systems:

Table 2.1 The study solutions and symbols

Symbols Composition of plating solution

Manufacture of catalytic core sets carrying Ni-CeO2-CuO coating

Two 430 ferrit steel roll billets were cut along the length of the roll to have a large length with a width of 25 mm, a thickness of 0.20

mm, in which one was used for forming laminating in length profile

of 6.5 m, another was used as buffer between two shaping layers with the length of 5 m) as shown in Figure 3.49, 3.51

Characteristics of catalyst:

- Catalytic core diameter: 120 mm

- Length: 100 mm (including 4 rolls)

- Gas contact surface area of catalytic core:

S = (Sflat plate + Sdeformation) x 2 = (5 x 0.025 + 6.5 x 0.025) x 2 x 4

= 2.3 m2

Figure 3.49 Specification of

workpiece preparation to

machine

Figure 3.51 Mold for rolled shape

Creating steel foil profile was made by forming laminating method

Figure 3.52 Rolling the steel foil on the jig to create a coating (a) and shaping together after coated the Ni-CeO 2 -CuO composite

plating (b)

2.3 The research methods

2.3.1 Research methods used to study the plating process

Cathodic potentiodynamic and electrochemical impedance spectroscopy

2.3.2 Methods and techniques used for evaluating the platings

- Scanning electron microscopy SEM, energy dispersive analyzer EDX, element mapping;

- Hardness measurement of plating; abrasion resistance measurement; characteristics of electrochemical corrosion of plating; platings thermal shock stability measurement; acceleration test assesses environmental durability

- Catalytic activity of the platings determined on the current reaction system:

Figure 2.3 Principle diagram for determining the catalytic ability of

platings on the micro-current reaction system

CHAPTER 3 RESULTS AND DISCUSSION 3.1.Properties of nano CuO and CeO2

3.1.1 Morphology

3.1.1.1 SEM and TEM images

SEM and TEM images of CuO and CeO2 particles showed that shape and size of these oxides were quite even

Figure 3.1 SEM images of nano paricles: CeO 2 (1a), CuO (1b); TEM

images of CuO (2a, 2b) and CeO 2 (2c, 2d)

CuO and CeO2 particles had nano size They were not in spherical form but often angular, that gave advantages in the process of burying particles into the plating layer

Hình 3.6 EDX results of CuO particles

3.1.2 Catalytic activity of CuO and CeO2 material particles for conversion of CO and CxHy gas from engine exhaust

Figure 3.7 The conversion degree of CO and C 3 H 6 gas of the CeO 2

and CuO materials

The catalytic activity of mixture of CeO2 and CuO was higher than the individual particle with the ability to convert CO gas got 100% at low temperature (300 oC) The catalytic ability for C3H6 gas conversion of CuO and CeO2 mixture reached 96.18% at 450 oC The conversion degree increased and kept stable at a high level in the temperature range of 200 oC to 500 oC This result showed that it is possible to use nano-sized CuO and CeO2 particles in the treatment

of CO, hydrocarbons in gasoline engine exhaust with high effective

3.2 Properties of sulphate solution containing CuO and CeO2 particles used to create Ni-CeO2-CuO composite coating

3.2.1 Cathodic polarization curves

Polarization curves showed that the polarization decreased as concentration of NiSO4 in solution increased Therefore, it was necessary to use a solution with a concentration of NiSO4 of about

250 ÷ 350 g/L The thesis chosed the electrolyte solution of NiSO4

300 g/L for further studies

Figure 3.9 Cathodic polarization curves

of nickel electrode in the electrolyte

solution of NiSO 4 (50 ÷ 350 g/L) +

H 3 BO 3 (30 g/L) + sodium lauryl sulphate

(0.1 g/L)

-0.4 -0.6 -0.8 -1.0 -1.2 -1.4 0.00

-0.04 -0.08 -0.12

-0.16 1- S 0

Figure 3.11 Cathodic polarization curves of nickel electrode in the electrolyte solutions: S 0 , S 0 Cu 8 , S 0 Ce 8

và S 0 Cu 4 Ce 4

The discharge potential of Ni2+ in the sulphate solution and in the composite plating solution were E* = -0.70 V (Ag/AgCl) and E* = -0.66 V (Ag/AgCl), respectively When CeO2 and CuO particles were added simultaneously to the sulphate solution, the cathode polarization increased reducing the cathode discharge current at a specific value of voltage, allowing plating with a smaller current density, thus reducing plating speed in composite plating solution CuO and CeO2 particles had changed the discharge capacity of

Ni2+ ions on cathode CuO and CeO2 particles tent to shift the polarization curves in the S0Cux, S0Cey solution to the negative side than that in the S0 bare solution The discharge current increased allowing plating at a higher current density in the S0CuxCey solution containing both CuO and CeO2 than in the solution containing only one kind of particles

-0.02 -0.04 -0.06 -0.08 -0.10 -0.12

Figure 3.12 Cathodic polarization

curves of nickel electrode in the

electrolyte solution S 0 Cu x (x = 2÷14)

Figure 3.13 Cathodic polarization curves of nickel electrode in the electrolyte solution S 0 Ce y (y = 2÷14)

polarization curves of nickel

electrode in the electrolyte

solution with different

concentrations of particles

0.00 -0.02 -0.04 -0.06 -0.08 -0.10

6 3 5

ratios of particles

Cathode polarization of nickel was almost unchanged with the CeO2 content in solutions changing from 2 to 12 g/L but increased as the amount of CeO2 particles in the solution increased to 14 g/L The cathode polarization did not change with 2 ÷ 6 g/L CuO and CeO2 in the solution, reached the smallest value with 8 g/L particles

in the solution and tended to increase as the particles in the solution increasing from 10 to 14 g/L

This can be explained by the fact that when the amount of particles in the solution increased to 10 ÷ 14 g/L, the CuO and CeO2

nanoparticles were more adsorbed by NiOH+ ions, reducing the amount of NiOH+ ions to the electrode surface, leading to a reduction

in the discharge rate and precipitation of metal ions, therefor cathode polarization increased

3.2.2 In-situ electrochemical impedance spectroscopy of the study electrode in sulphate-plating solutions

For sulphate plating solution:

The Nyquist electrochemical impedance spectroscopies of the study electrode in S0 solution at different voltages and the corresponding equivalent circuit to that impedance spectrums were shown in Figure 3.10 and Figure 3.11, respectively

Figure 3.16 Nyquist

Table 3.1 The values of elements in equivalent circuit of study

electrode in S o solution at different voltages

H2 gas released on the cathode caused by reducing the Ni-Hadsorption

molecule on the electrode surface, and the reduction of NiOH+ ions was also more powerful

For sulphate plating solution containing CuO particles:

Table 3.3 The values of elements in equivalent circuit of study electrode in S 0 Cu 6

, S 0 Cu 8 solutions at -0.704 V và -0.834 V

0Cu6 solution S0Cu8 solution -0.704 V -0.834 V -0.704 V -0.834 V

For sulphate plating solution containing CeO 2 particles:

The Nyquist electrochemical impedance spectroscopies of the study electrode in S0Ce6 và S0Ce8 solutions at -0.704 V and -0.834 V were shown in figure 3.21, in which solid lines were simulated lines, symbols were experimental points This result showed that in the electroplating process, there was an inductance component that characteristic for adsorption process on cathode surfaces, but there wasn’t diffusion one This phenomenon was similar to that in the S0

solution as well as in the S0Cux solution

0 200 400 600 800 1000 1200 1400 0

100 200 300 400 500

Table 3.5 The values of elements in equivalent circuit of study electrode in S 0 Ce 6 and S 0 Ce 8 solutions at -0.704 V và -0.834 V

The Nyquist electrochemical impedance spectroscopies of the study electrode in S0Cu4Ce4 solution at different voltages (-0.704 V, -0.834 V and -0.964 V) were shown in figure 3.23, in which solid lines were simulated lines, symbols were experimental points

Figure 3.23 Nyquist electrochemical

impedance spectroscopies of the

study electrode in S 0 Cu 4 Ce 4 solution

Table 3.7 The values of elements in equivalent circuit of study electrode in S 0 Cu 4 Ce 4 solution at different voltages

-0.704 4.57 54.70 0.79 32.22 98.02 25.05 -0.834 4.41 55.48 0.82 4.62 27.99 0.51 -0.964 4.32 43.96 0.67 3.33 63.08 0.07

The results showed that the adsorption resistance was much larger than charge transfer resistance at all three voltages proving that two processes that were charge transfer and adsorption of NiOH+ ions took place simultaneously but the adsorption process controlled