What is the Smallest Particle Representing Hydrogen Peroxide

What is the Smallest Particle Representing Hydrogen Peroxide.

Effects of hydrogen peroxide co-precipitation and inert N
ii

atmosphere calcination on CeZrLaNd mixed oxides and the catalytic functioning used on Pd supported 3-way catalysts

Received 9th February 2019

, Accepted 6th March 2019

Outset published on twelfth March 2019


Abstruse

The unique reversible oxygen storage and release capacity of cerium zirconium mixed oxides makes them ideal washcoat materials of automotive 3-way catalysts (TWC). In this piece of work, cerium zirconium mixed oxides of Ce
0.15
Zr
0.79
La
0.02
Nd
0.04
O
2

were prepared
via
a co-atmospheric precipitation method. The effects of hydrogen peroxide co-precipitation and inert North
ii

temper calcination on the structure and properties of cerium zirconium mixed oxides were investigated systematically by Brunauer–Emmett–Teller surface area measurements, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, hydrogen temperature-programmed reduction, oxygen storage capacity (OSC), Raman spectroscopy, and X-ray photoelectron spectroscopy. Additionally, the catalytic performance of palladium supported catalysts was studied. Results prove that hydrogen peroxide co-precipitation promotes the dispersion of cerium zirconium particles and enhances crystal grain growth, resulting in good thermal stability of the obtained cerium zirconium mixed oxides. Inert N
2

atmosphere calcination also enhances the dispersion of particles, results in smaller and finer crystal grains, enriches pore channels, and significantly improves the surface expanse, pore volume and OSC, with an OSC of 424.57 μmolO
2

g
−1
, which is a 13.37% increment compared with the common sample. The benefits of hydrogen peroxide co-precipitation and inert Northward
two

atmosphere calcination endow the Pd supported catalysts of cerium zirconium mixed oxides with adept three-style catalytic performance.


1. Introduction

Cerium zirconium mixed oxides accept unique reversible oxygen storage and release capacity and are therefore a topic of nifty involvement to researchers.
ane–three

They are widely used in automotive three-way catalysts (TWC) as key washcoat materials.
4

Large area, good thermal stability and loftier oxygen storage capacity (OSC) are the fundamental properties of cerium zirconium materials for TWC applications.
five

The basic principle is the redox couple of Ce
3+
/Ce
4+

in the CeO
ii
. It has been proven that Zr
four+

cations intensively promote the mobility of oxygen ions and enhance the oxygen storage capacity.
half dozen,seven

Previous works take shown that thermal stability can be improved by introducing organic additives.
8

OSC can be improved by using mesoporous cerium zirconium mixed oxides with hard template methods.
9

Another technique involves the introduction of dopants, such as rare earths,
x–12

transition metals,
13,14

and alkaline earth metals,
xv

to stabilize construction, improve OSC, and improve heat resistance. Ce has two valences, only the ion radii of Ce
three+

(0.114 nm) and Ce
four+

(0.097 nm) differ drastically,
16

and the co-precipitation pH values are also different. The ion radii of Ce
4+

and Zr
iv+

(0.084 nm) are somewhat similar, and their co-precipitation pH values are also similar. The solubility product abiding (K

sp
) of Ce(OH)
3

is 1.5 × 10
−20

and is very different from that of Zr(OH)
4
, which is 2.0 × 10
−48
. The solubility product constant (Yard

sp
) of Ce(OH)
four

is 4 × 10
−51
, which is very close to that of the Zr(OH)
four
.
17

Therefore, the valance of Ce ion affects the cerium zirconium mixed oxides. Many studies are currently focused on high-free energy mechanical milling,
xviii

template assisted,
19

hydrothermal treatment,
20

microemulsion,
21

and supercritical alcohols,
22

for the process of preparing cerium zirconium mixed oxides. However, the calcination procedure, and even the inert atmosphere calcination have not been extensively studied.

In this study, Ce
0.fifteen
Zr
0.79
La
0.02
Nd
0.04
O
2

cerium zirconium mixed oxides were synthesized past a co-atmospheric precipitation method. Hydrogen peroxide was introduced to change the Ce ion valence from Ce
three+

to Ce
4+
. Inert North
ii

atmosphere calcination was carried out to provide an oxygen-deficient atmosphere to modify the precipitate precursors’ hydrolysis process. The effects of hydrogen peroxide co-precipitation and inert N
2

atmosphere calcination on the structure and properties of CeZrLaNd mixed oxides were investigated systematically by means of Brunauer–Emmett–Teller (BET) surface area measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), manual electron microscopy (TEM), hydrogen temperature-programmed reduction (H
2
-TPR), oxygen storage capacity (OSC), Raman spectroscopy and 10-ray photoelectron spectroscopy (XPS). Furthermore, the three-mode catalytic operation of palladium supported catalysts was also studied. Hydrogen peroxide co-precipitation promotes particle dispersion, enhances crystal grain growth, and shows good thermal stability. Inert Northward
two

atmosphere calcination results in effectively and smaller crystal grains, enriches pore channels, and significantly improves surface area, pore volume and OSC. The benefits of hydrogen peroxide co-atmospheric precipitation and inert Due north
2

atmosphere calcination endow the Pd supported catalyst of cerium zirconium mixed oxides with good three-style catalytic performance.

ii. Experimental

ii.1 Materials preparation

Ce
0.xv
Zr
0.79
La
0.02
Nd
0.04
O
ii

mixed oxides were prepared with a co-atmospheric precipitation method. The CeCl
3
, ZrOCl
two
, LaCl
three

and NdCl
3

solutions were stirred well at a Ce[thin space (1/6-em)]:[thin space (1/6-em)]Zr[thin space (1/6-em)]:[thin space (1/6-em)]La[thin space (1/6-em)]:[thin space (1/6-em)]Nd molar ratio of 15[thin space (1/6-em)]:[thin space (1/6-em)]79[thin space (1/6-em)]:[thin space (1/6-em)]2[thin space (1/6-em)]:[thin space (1/6-em)]4. The higher up metallic mixture was precipitated by a 2.5 mol 50
−1

sodium hydroxide solution. Filtration was followed past deionized water washing, organic additive introduction, and filtration once over again. The wet filter block was then dried at 120 °C for 12 h, so calcined in a muffle furnace at 800 °C for 3 h to prepare a fresh sample, which was labelled as CZLN-f. In a contrasting experiment, during the co-precipitation, hydrogen peroxide (H
2
O
2
) was introduced, and its mole ratio to Ce
iii+

was 0.5. The other steps are the aforementioned as the procedure higher up. The related fresh sample was labelled as CZLN-H-f. In the tertiary experiment, the stale filter cake (no H
ii
O
2

introduction) was firstly calcinated in an inert North
two

atmosphere at 800 °C for iii h, then calcinated in air at 450 °C for two h. The obtained fresh sample was labelled every bit CZLN-N-f. To obtain corresponding aged samples, all fresh samples were calcined at thou °C for four h to evaluate their thermal stability, and denoted as CZLN-a, CZLN-H-a and CZLN-N-a, respectively.

two.ii Catalyst preparation

0.5 wt% Pd loading catalysts were prepared
via
an incipient wetness impregnation method. Briefly, the CZLN-f, CZLN-H-f and CZLN-N-f powders were impregnated with a Pd(NO
3
)
two

solution, separately. Then, the wet powders were dried at 105 °C overnight, and calcinated at 500 °C for ii h to obtain fresh catalysts, denoted every bit Pd/CZLN-f, Pd/CZLN-H-f and Pd/CZLN-Northward-f. The fresh catalysts were calcined at 1000 °C for 4 h to prepare the aged samples, and recorded equally Pd/CZLN-a, Pd/CZLN-H-a and Pd/CZLN-N-a, respectively. The higher up catalysts were pressed into tablets, then crushed and sieved to twoscore–60 mesh pellets earlier catalytic evaluation.

2.iii Powder characterization techniques

North
2

adsorption/desorption was used to detect the surface expanse, pore book, and pore diameter distribution of the samples at 77 K measured past Quadrasorb SI-KR/4MP (Quantachrome Instruments, USA). Before measurement, samples were degassed in a vacuum at 280 °C for 3 h. XRD spectra were recorded with holland PANalytical X’Pert PRO MPD using Cu Kα, with a step of 0.02°. The generator voltage was prepare to twoscore kV and electric current set 40 mA. The morphology of the samples was observed using a Hitachi SEM (Japan). Micro-structures of the samples were further observed by TEM using a Tecnai G
2

F20 S-TWIN TEM (FEI Visitor, United states, 200 kV accelerating voltage). OSC and H
2
-TPR of samples were measured with a Chembet PULSAR TPR/TPD instrument (United states of america). The samples were pretreated in 10% H
ii
/Ar at 800 °C for 1 h, and and then oxidized at 500 °C past periodically and automatically injecting 289 μL pure O
two

gas at an interval of well-nigh 5 min to measure OSC. For the H
2
-TPR testing, the samples were beginning pretreated at 550 °C for 0.5 h with a gas flow of 5 vol% O
2
/Ar. Then, pure He gas was switched into the pipeline to sweep the samples for 30 min, and cooled to room temperature. The gas flow of 10% H
2
/Ar was then switched into the system. The samples were afterwards heated upwardly to 900 °C at a rate of 5 °C min
−one
. Raman spectra were measured using a Lab Spectrum Raman spectrometer at a laser wavelength of 532 nm (Horiba, Japan). The detecting frequency range was 100–1500 cm
−1
. The chemical weather of the surface were analyzed by ESCALAB 250Xi X-ray photoelectron spectroscopy (XPS) nether 6.7 × x
−eight

Pa (ThermoFisher Scientific, USA). The working voltage and current were 14 kV and xx mA, respectively.

2.4 Catalytic performance evaluation

The three-fashion catalytic functioning was evaluated in a fixed-bed reactor with a simulated exhaust gas mixture of NO (900 ppm), HC (900 ppm), CO (1.5%), CO
ii

(12%), O
ii

(1.2%) and Due north
2

(remainder). A 0.6 mL of pellet Pd supported catalyst (twoscore–lx mesh) and 0.3 mL of quartz sand (40–60 mesh) were mixed well and loaded into the fixed-bed quartz reaction tube. The two sides of the quartz tube were plugged with quartz fiber. The GHSV was 50[thin space (1/6-em)]000 h
−1
. The out gases were analyzed past a multi-gas infrared analysis instrument (MKS, U.s.a.). The three-way catalytic performance evaluations were carried out at the platonic air/fuel ratio. The temperature of catalyst was increased from room temperature to 450 °C at a rate of v °C min
−one
.

iii. Results and discussion

3.1 BET analysis

As shown in Tabular array i, compared with the fresh common sample, hydrogen peroxide co-precipitation lowers the fresh surface area and pore volume; withal, the inert North
2

atmosphere calcination sample presents the largest fresh surface area of 103.67 m
2

g
−1
, with a 35.52% increase. The CZLN-N-f also shows a high pore book of 0.6250 mL g
−1
, with an increment of 26.31%. Information technology is revealed that the inert Due north
2

atmosphere enhances the surface expanse and pore book. After thermal treatment at 1000 °C for 4 h, all cerium zirconium mixed oxides notwithstanding have large surface area and pore volume, of which the CZLN-a shows the largest surface area of 46.70 m
2

g
−ane
, and CZLN-H-a presents the biggest pore volume of 0.4256 mL g
−one
. Moreover, the surface expanse reduction of CZLN-H-a compared with the fresh sample is the lowest at 32.5%, 38.9% for a common sample, and 57.ane% for the N
ii

atmosphere calcination sample. The anile surface area and pore volume of CZLN-N-a are lower than that of CZLN-a. From the in a higher place statement, information technology can be deduced that the hydrogen peroxide co-precipitation improves the loftier temperature thermal stability of the cerium zirconium mixed oxides. The inert N
ii

atmosphere greatly improves the fresh surface area and pore volume, however information technology lowers the thermal stability. During inert N
2

calcination, the organic additives changes to solid carbons by carbonization because of the absence of oxygen. The precursor gets to cerium zirconium mixed oxides on the surface or the environment of the solid carbons. All these solid carbons are removed by the next low temperature air calcination, leaving backside large pores inside the mixed oxides, resulting in a sample with loftier surface expanse and large pore volume. Even so, after four h heating handling at yard °C, big parts of pores are collapsed or disappeared, leading to a smaller surface area and pore book. The thermal stability of hydrogen peroxide co-precipitation sample can exist explained past the fact that hydrogen peroxide changed the Ce
3+

to Ce
four+
, and the Ce
4+

and Zr
4+

co-precipitated at the aforementioned time, thereby improving the solubility of the cerium zirconium mixed oxides, leading to a stable construction and good thermal stability.

Tabular array 1
BET surface area, pore volume, and pore size of samples

a


Sample Specific surface area (m
2

g
−ane
)
Total pore book (mL grand
−1
)
Average pore size (nm) BJH pore size (nm) ΔS

BET

(%)
a
ΔS

BET

is calculated past (expanse of fresh sample − expanse of aged sample)/surface expanse of fresh sample × 100%.
CZLN-f 76.50 0.4948 25.87 thirty.40
CZLN-H-f 64.00 0.4340 25.25 17.15
CZLN-N-f 103.67 0.6250 24.12 thirty.69
CZLN-a 46.seventy 0.3173 27.18 thirty.48 38.9
CZLN-H-a 43.xix 0.4256 39.41 30.71 32.5
CZLN-N-a 44.52 0.3089 27.75 thirty.05 57.i

In Fig. ane, the North
2

adsorption and desorption curves of all samples show type 4 with a blazon H1 hysteresis hoop, which indicates that mesopores be in CZLN mixed oxides.
23

For fresh samples, the area of the hysteresis loop of CZLN-N-f is the largest. For the aged samples, the area of CZLN-H-a is the largest. It is in accordance with the BET results of pore book listed in Table 1. Information technology is also further revealed that inert North
2

atmosphere calcination has good pore enriched and enlarged effects, leading to large pore book and high surface expanse. The hydrogen peroxide co-atmospheric precipitation is helpful to improve the thermal stability of cerium zirconium mixed oxides. From the inset graph, it can be seen that the pore distribution of the samples have different pore size distribution curves. For CZLN-f and CZLN-N-f samples, the highest points of pore distribution curves are centered at about thirty nm, while for CZLN-H-f, the highest point of pore distribution curve is centered at almost 17 nm. After m °C thermal aging treatment, for all the anile samples, the highest points of pore distribution curves are centered at xxx nm. The results are similar to the BJH pore size listed in Table 1.

image file: c9ra01048c-f1.tif
Fig. 1


The North
ii

adsorption and desorption curves of samples (“f” denotes fresh and “a” denotes aged samples).

3.ii XRD assay

It can exist seen from Fig. 2f that all fresh samples show a complete crystal construction with high solid solubility, present a single phase. The phase construction is a tetragonal phase of Ce
0.12
Zr
0.88
O
two

with a
Piv
2
/nmc
infinite group (reference lawmaking: 01-089-9067). No La and Nd oxides peaks are plant in the Ten-ray diffraction blueprint, indicating that the doped La and Nd are highly dispersed in the cerium zirconium lattice, and at the same time cerium oxide and zirconium oxide are combined to form a homogeneous solid solution.
24

In add-on, CZLN-N-f exhibits the widest diffraction peaks, indicating that the smallest crystal size is five.vii nm (listed in Table two). The CZLN-H-f however, has the biggest crystal size of 8.eight nm, which reveals that the hydrogen peroxide co-atmospheric precipitation improves the crystal growth of cerium zirconium mixed oxides.

image file: c9ra01048c-f2.tif
Fig. two


XRD diffraction spectra of samples.“f” denotes fresh and “a” denotes aged samples, respectively.

Table ii
Structural parameters and grain sizes of fresh and aged samples

a


Sample (101) airplane Lattice parameter (Å) Grain size (nm) Δ
GS

(%)
2θ
(°)
D
(Å)
{101}
a
Δ
GS

(%): percentage grain growth compared with the fresh state, Δ
GS

(%) = {GS(aged) − GS(fresh)/GS(fresh)} × 100%.
CZLN-f 29.802 2.9955 v.1878 7.8
CZLN-H-f 29.789 2.9967 5.1907 8.8
CZLN-North-f 29.769 2.9987 5.1937 5.vii
CZLN-a 29.763 2.9993 5.1948 14.6 87.18
CZLN-H-a 29.778 2.9978 v.1924 14.8 68.18
CZLN-N-a 29.789 ii.9967 5.1905 14.6 156.fourteen

After thermal aging treatment at thousand °C for four h, the XRD peaks of all samples sharpens and narrows, showing that the size of the crystals increases continuously during the process. The fresh peaks are half-dozen–9 nm, and the aged ones are 15 nm. The increment percentage in the size of the CZLN-H-a grain is the everyman, at 68.18%, compared with CZLN-a (87.18%) and CZLN-North-a (156.xiv%). This further proves that the hydrogen peroxide co-precipitation causes the formation of the big-sized crystals, thereby increasing its thermal stability of crystal structure. Furthermore, Fig. 2a shows that the crystal phase of the aged samples is the same every bit that of the fresh ones, with no other phases present. Information technology besides shows the tetragonal stage construction of Ce
0.12
Zr
0.88
O
two
.

3.3 H
2
-TPR and oxygen storage chapters

Fig. 3f shows that the H
two
-TPR reduction curves of fresh cerium zirconium materials are similar and include two reduction peaks. The peak at low temperature corresponds to the reduction of surface and adsorptive oxygen of CeO
2
, while the superlative at high temperature represents the reduction of lattice oxygen of CeO
2
.
25,26

For the fresh samples, CZLN-Northward-f has the best reduction performance, with the smallest surface oxygen reduction temperature of 306.vii °C and the smallest lattice oxygen reduction temperature of 546.two °C, mainly due to its pore book being the largest and its surface area being the most significant. CZLN-H-f has a lower surface oxygen reduction temperature compared with CZLN-f, just the lattice oxygen reduction temperature is a little higher and thus the hydrogen peroxide co-atmospheric precipitation improves the surface oxygen reduction.

image file: c9ra01048c-f3.tif
Fig. 3


H
2
-TPR curves of samples. “f” and “a” denote “fresh” and “aged” samples, respectively.

As seen in Fig. 3a, after thermal aging at one thousand °C for 4 h, the aged samples show the same type of TPR curves equally the fresh ones, with two reduction peaks distributed in low and high temperature regions, corresponding to the reduction of surface, adsorptive oxygen of CeO
2

and the reduction of lattice oxygen of CeO
2
, respectively. The CZLN-N-a has the lowest surface oxygen reduction temperature of 298.8 °C, simply its lattice oxygen reduction temperature is the highest. This shows that inert N
2

atmosphere calcination enhances the surface oxygen reduction of the aged sample simply has no adept effect on its lattice oxygen reduction because of the small surface expanse and particles sintering of the aged inert North
2

atmosphere sample. The reduction curves of CZLN-H-a and CZLN-a take some similarities, revealing that hydrogen peroxide co-precipitation has no obvious effect on the oxygen reduction performance in the aged samples.

OSC data are listed in Table three. The prepared materials all take large oxygen storage chapters of more than 330 μmolO
ii

g
−1

in fresh samples and over 320 μmolO
2

thousand
−1

in aged samples. CZLN-North-f has the highest oxygen storage chapters of 424.57 μmolO
2

grand
−i
, which is a 13.37% increment compared with the mutual CZLN-f. This indicates that inert N
2

atmosphere calcination causes a significant and high comeback in the OSC of fresh samples because of their high surface surface area and large pore volume and good oxygen mobility. However, CZLN-H-f has the lowest OSC, 337.29 μmolO
2

grand
−1
, which is a nine.94% reduction compared with the CZLN-f. Afterward being aged for iv h at thou °C, CZLN-N-a withal has the highest the OSC value, 342.57 μmolO
2

grand
−1
, which is an increase of 5.76% compared with CZLN-a. In addition, CZLN-H-a has the lowest reduction in the OSC (iv.04%) compared with the related fresh samples, which further revealing that hydrogen peroxide co-precipitation improves the thermal stability, permitting the maintenance of a stable construction.

Table 3
Oxygen storage chapters of the samples

a



three.four SEM and TEM analyses

The morphologies of the samples were observed from the SEM images displayed in Fig. 4, which testify that the cerium zirconium mixed oxides obtained all take fine sphere-like particles. The CZLN-f sample is more aggregated and the porosity is somewhat smaller. CZLN-H-f and CZLN-N-f both have good particle dispersion, arable pore channels, and uniform spherical particles. The hydrogen peroxide and inert N
two

atmosphere calcination appears to promote the dispersion of cerium zirconium solid solution particles, causing the germination of rich pore channels. Furthermore, the inert N
2

calcination sample has the smallest particles, which may further improve its surface expanse.

image file: c9ra01048c-f4.tif
Fig. four


SEM images of the samples.

Fig. 5 shows that cerium zirconium samples all have skilful dispersion and pore structure. CZLN-N-f has the smallest grain size, the most compatible crystals, and the largest pore size. From particle distribution in Fig. five, the mean particle size of CZLN-Due north-f is the smallest at 6.0 nm, and that of CZLN-H-f is the largest at ix.ix nm. These are well in accord with the XRD results. This conspicuously reveals that inert N
2

atmosphere calcination has good result in reducing grain size, and enlarging pores, endowing the sample with a large surface area and pore volume.

image file: c9ra01048c-f5.tif
Fig. 5


TEM images of the samples.

3.v Raman spectra

In Fig. 6f, the fresh samples bear witness obvious adsorption peaks at 464 cm
−1
. These can exist attributed to the vibration of F
2g
, which corresponds to the cubic phase structure. The pinnacle centered at 618 cm
−1

corresponds to the non-degenerate LO manner vibration caused by the relaxation of symmetry rules, which is related to lattice defects and oxygen vacancies in the construction of cerium oxide.
27

The relative intensities of these vibration peaks are related to oxygen vacancy concentrations in the lattice of the cerium zirconium materials. This oxygen vacancy concentration is defined as the ratio of the vibration summit surface area at 618 cm
−1

and 464 cm
−i

(A

618
/A

464
). The larger the ratio, the higher the concentration of oxygen vacancies. The
A

618
/A

464

value of CZLN-N-f is the highest, at i.61, and that of CZLN-H-f is somewhat higher than that of CZLN-f. This ways that inert North
two

atmosphere calcination greatly improves the oxygen vacancies and leads to a high redox performance. Furthermore, hydrogen peroxide co-precipitation has good effect on enhancing the oxygen vacancies of the cerium zirconium mixed oxides. At that place are also some vibration peaks at 200–400 cm
−1
; these are attributed mainly to the tetragonal structure of zirconia and the commutation of the cerium oxide lattice to class oxygen vacancies.
28

image file: c9ra01048c-f6.tif
Fig. 6


Raman spectra of samples. “f” and “a” denote fresh and aged samples, respectively.

In the same way, in Fig. 6a, the aged samples nowadays obvious adsorption peaks at 484 cm
−1

and these can exist ascribed to the vibration of the F
2g

mode corresponding to the cubic phase construction. The top centered at 628 cm
−1

corresponds to the not-degenerate LO vibration mode caused by the symmetric relaxation related to lattice defects and oxygen vacancies in the construction of cerium oxide. The oxygen vacancy concentration of the aged samples is defined as the ratio of the vibration peak area at 628 cm
−1

and 484 cm
−1

(A

628
/A

484
). The
A

628
/A

484

value of CZLN-N-a, one.77, is the largest and that of CZLN-f, 1.72, is the smallest. Therefore, both inert Due north
2

atmosphere calcination and hydrogen peroxide co-precipitation improve the oxygen vacancies of the aged samples.

3.6 XPS spectra

The XPS spectra of samples are shown in Fig. vii and eight, and can be used to explore the distribution of the elements on the surface of samples. The Ce/Zr molar ratio in the raw materials was designed as 0.19. However, as Table 4 shows, the Ce/Zr ratio of the fresh samples are all less than this value. The increase in Zr concentration on the surface suggests that cerium ions tend to migrate to the bulk phase, of which the Ce/Zr of CZLN-Northward-f decreases the most. This reveals that inert Due north
2

temper calcination promotes cerium migration into the inner majority. For the aged samples, the Ce/Zr is higher than that of the related fresh samples, revealing that the cerium ions tend to drift back to the surfaces of the samples during the thermal handling.

image file: c9ra01048c-f7.tif
Fig. seven


Ce 3d spectra for the samples. “f” and “a” denote fresh and aged samples, respectively.

image file: c9ra01048c-f8.tif
Fig. 8


O 1s spectra for samples. “f” and “a” denote fresh and anile samples, respectively.

Table iv
Results of XPS analysis of the surfaces of the samples

a


Samples Ce/Zr Ce
3+
/(Ce
3+

+ Ce
4+
)
O
β
/(O
α

+ O
β

+ O
γ
)
a
The theoretical designed molar ratio of Ce/Zr in raw materials is 0.19. “f”: fresh sample; “a”: aged sample.
CZLN-f 0.1175 29.39 0.6107
CZLN-H-f 0.1242 23.76 0.4817
CZLN-N-f 0.1118 23.21 0.7828
CZLN-a 0.1298 21.76 0.6062
CZLN-N-a 0.1243 22.19 0.5322

The oxidation states of Ce were analyzed by acme plumbing fixtures the curves of the Ce 3d spectra. As shown in Fig. 7, these curves are equanimous of 8 peaks corresponding to four pairs of spin–orbit doublets. The peaks labelled “u” and “v” stand for the spin-orbits of Ce 3d
3/2

and Ce 3d
v/2
, respectively. The peaks marked v′ and u′ correspond the initial electron state 3d
ten
4f
1
, which corresponds to Ce
3+
. The proportion of Ce
3+

species (v′, u′) in terms of the full cerium species tin can be obtained from the ratio of the sum of the area of Ce
3+

species to the sum of the area of the total cerium species.
29,xxx

Tabular array 4 shows that CZLN-f has the highest surface Ce
3+

ratio. Later the thermal handling, the value of Ce
3+
/(Ce
3+

+ Ce
4+
) is somewhat lower than that of the related fresh sample, which is attributed to the reduction in the surface of Ce
iii+

caused by the oxidation of Ce
3+

to Ce
iv+
.

O 1s XPS spectra are always used to distinguish the state of surface oxygen species. The O 1s spectra of all samples are fitted into three peaks. Three oxygen species can be identified, as shown in Fig. eight. Peak α can be attributed to lattice oxygen O
2


2−
, tiptop β to surface adsorbed oxygen O
ii−
, O

, OH


or oxygen vacancies, and acme γ likely to adsorbed molecular water.
31–33

Surface oxygen species have a relatively high reactivity owing to their high mobility. As shown in Table 4, CZLN-N-f has the biggest value of O
β
/(O
α

+ O
β

+ O
γ
), i that is much higher than that of CZLN-f and CZLN-H-f. This indicates that inert Northward
2

atmosphere calcination greatly improves the surface oxygen species and the redox performance due to the not bad surface area and pocket-sized particle size of CZLN-North-f. After thermal treatment, the O
β
/(O
α

+ O
β

+ O
γ
) value of CZLN-N-a is reduced to less than that of CZLN-f because of the large reduction in surface surface area and pore volume and large increase in grain size of the aged sample.

3.7 Catalytic performance

The three-way catalytic functioning of the fresh and aged palladium supported catalysts were evaluated at the idea air/fuel ratio.
T

50

represents the calorie-free-off temperatures of the catalyst, defined as the respective catalyst temperature when the conversion reaches 50% for CO, C
3
H
eight
, and NO, respectively.
T

90

represents the total conversion temperature of the catalyst, divers as the corresponding catalyst temperature when the conversion up to xc% for CO, C
three
H
eight
, and NO, respectively. As Fig. nine and Table 5 bear witness, Pd/CZLN-N-f has the all-time CO catalytic conversion, with the lowest calorie-free-off temperature
T

50-CO

of 218 °C (a reduction by 13 °C compared with the common fresh sample Pd/CZLN-f) and the lowest full conversion temperature
T

xc-CO

of 231 °C (a reduction past 8 °C compared with the common fresh sample Pd/CZLN-f). This reveals that inert N
2

atmosphere calcination promotes CO conversion greatly because of its large area, high OSC, and adept redox properties. However, CZLN-H-f has the all-time catalytic performance for C
3
H
8
, with the everyman low-cal-off temperature
T

50-C
3
H
8



of 302 °C (a reduction by 13 °C compared with the common fresh sample Pd/CZLN-f) and the lowest full conversion temperature
T

xc-C
three
H
eight



of 342 °C (a reduction by twenty °C compared with the common fresh sample Pd/CZLN-f). CZLN-H-f also has the best catalytic performance for NO conversion, with the everyman
T

50-NO

and
T

xc-NO
, being reduced by more than than 33 °C and by 14 °C, respectively, compared with the common fresh sample Pd/CZLN-f. This reveals that hydrogen peroxide co-precipitation enhances the catalytic conversion of C
iii
H
8

and NO of the fresh samples. Information technology is shown that at that place are some oscillations in the conversion curves at 200–300 °C for NO conversion; these are perhaps mainly caused by the weaker NO reduction capacity of Pd compared with that of Rh.
34

image file: c9ra01048c-f9.tif
Fig. ix


Iii-style catalytic performance of fresh Pd supported catalysts. “f” is denoted every bit fresh samples.

Table v
The light-off and total conversion temperature of fresh Pd supported catalysts

a


Samples T

50

(°C)
T

90

(°C)
CO C
three
H
8
NO CO C
3
H
8
NO
a

T

50

stands for calorie-free-off temperature, defined as the temperature at conversion of 50%.
T

90

stands for total conversion temperature, divers as the temperature at conversion of 90%.
Pd/CZLN-f 231 315 240, 360 239 362 362
Pd/CZLN-H-f 232 302 239, 327 239 342 348
Pd/CZLN-Due north-f 218 321 232, 359 231 378 381

Fig. ten and Table 6 testify that for palladium supported catalysts thermally aged at thousand °C, Pd/CZLN-North-a has the all-time three-way catalytic conversion, with the lowest low-cal-off temperature
T

l-CO

of 243 °C,
T

50-C
iii
H
8



of 389 °C,
T

50-NO

of 389 °C; which are reductions past 14 °C, 17 °C, and 53 °C, respectively, compared with the common aged Pd/CZLN-a. Additionally, Pd/CZLN-Northward-a has the lowest total conversion temperature
T

90-CO

of 247 °C,
T

90-C
3
H
8



of 391 °C, and
T

xc-NO

of 391 °C, respectively; these are reductions by 12 °C for CO and past 63 °C for C
3
H
8
, compared with the mutual aged Pd/CZLN-a. This reveals that inert North
ii

atmosphere calcination promotes the three-style catalytic performance of the thermally anile catalysts, mainly due to its great oxygen storage capacity, redox operation and abundant oxygen vacancies even later on being thermally aged at 1000 °C.

image file: c9ra01048c-f10.tif
Fig. 10


Three-way catalytic operation of aged Pd-supported catalysts. “a” is denoted equally anile samples.

Table 6
The
T

l

and
T

90

of Pd supported catalysts aged at one thousand °C

Samples T

l

(°C)
T

90

(°C)
CO C
3
H
8
NO CO C
iii
H
8
NO
Pd/CZLN-a 257 406 442 259 454
Pd/CZLN-H-a 244 402 415 256 436 438
Pd/CZLN-N-a 243 389 389 247 391 391

four. Conclusions

In this study, Ce
0.15
Zr
0.79
La
0.02
Nd
0.04
O
2

cerium zirconium mixed oxides with high surface areas and pore volumes were prepared using a co-atmospheric precipitation method. Hydrogen peroxide co-precipitation and inert N
2

atmosphere calcination have great influence on the structure and properties of cerium zirconium materials. The quondam promotes the dispersion of cerium zirconium particles and enhances growth of the crystal grain, causing the obtained cerium zirconium mixed oxides to take a adept thermal stability. The surface surface area of a sample aged at k °C for 4 h is 43.19 m
2

1000
−one
, and it has the everyman reduction in surface area (32.5%) compared with the fresh sample. Inert North
2

temper calcination also enhances the dispersion of particles, moreover making the crystal grains fine and small, and enriching pore channels, leading to significantly big surface areas and pore volumes. In addition, it greatly improves the redox operation and oxygen storage capacity of the material, with OSC of 424.57 μmolO
2

g
−1

(a 13.37% increment compared with the common CZLN-f) caused by abundant oxygen vacancies, much surface and majority oxygen species. For fresh Pd supported catalysts, Pd/CZLN-H-f has the best catalytic performance for C
3
H
8

and NO conversion, reducing
T

fifty-C
three
H
8



by 13 °C and
T

l-NO

by 33 °C compared with the common fresh sample Pd/CZLN-f. Pd/CZLN-North-f has the best CO catalytic conversion, reducing
T

l-CO

past 13 °C and
T

90-CO

past 8 °C compared with the common fresh sample Pd/CZLN-f. For the Pd-supported catalysts thermally anile at 1000 °C, inert N
2

atmosphere calcination conspicuously and significantly enhances three-fashion catalytic performance. Pd/CZLN-N-a is the best catalyst, with a
T

50-CO

reduction by 14 °C, a
T

50-C
3
H
eight



reduction by 17 °C, and a
T

50-NO

reduction by 53 °C, compared with the mutual aged sample CZLN-a. This is mainly due to its nifty oxygen storage capacity and abundant oxygen vacancies, even later thermally anile at g °C.

Conflicts of interest

There are no conflicts of interest to declare.

Acknowledgements

This work is financially supported by the China National Key Enquiry and Development Program (No. 2017YFC0211002).

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What is the Smallest Particle Representing Hydrogen Peroxide

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