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A Simulation Study for Trimetallic Nanosized Alloy (Ni, Cu, and Ag) in Hydrogenation of Organic Compounds: A Case Study of "Nitrophenols".

1. Introduction

Hydrogenation reactions are one of the most important reactions for preparation of many fine chemicals and important intermediates [1-5]. The selectivity and activity of such reactions are an issue of most recent researches [1,2]. Most of catalysts used in such important reactions are metal catalysts [6, 7]. The basic idea of hydrogenation reactions is to adsorb both metal and target organic moiety subject to hydrogenation. The challenge in this subject is to find that metal has high activity and selectivity towards the desired compound. In order to attain both activity and selectivity researches tend to use bimetallic system. Thus, a combination of Ni-Ag, Ni-Cu, and Ni-Au was used in [1] for active and selective hydrogenation of cinnamaldehyde. In addition, Ni-Pd bimetallic system was used in hydrogenation of nitrobenzyl ethers to amino benzyl [2]. Moreover, Ni-Ag bimetallic system was used in hydrogenation of dimethyl oxalate [3]. Many others researches also used many combinations of bimetallic systems in order to enhance the selectivity and activity [4-8]. Searching the literature data, only few papers deal with the trimetallic system. Thus, in [9] homogenous catalyst containing trimetallic system of Sn, Ru, Pt in selective reduction of cyclodecatriene. However heterogeneous catalyst containing clusters of Pt[Ru.sub.5]Sn was evaluated as hydrogenation catalyst [10, 11]. Just as rare sole example we found a paper that deals with hetero quarter metallic nanoparticle hydrogenation catalyst of Ni/Ru/Pt/Au [12]. In all above examples of hydrogenation catalysts containing bi- or tri- or even quaternary metallic systems a simple evaluation of one sample or more is performed just to bring the selectivity and compare it to bi- or monometallic catalyst. In this paper we aim to investigate and write a mathematical simulation program containing trimetallic heterogeneous catalyst containing Ni, Ag, and Cu.

In order to fulfill this purpose, we choose a simple effective hydrogenation reaction. Thus hydrogenation of nitrophenol into amino phenol using supported metal and using hydrazine hydrate as a hydrogen source was proven to be 100% selective and finishes with 100% conversion in only few minutes [13,14]. The program will evaluate the effect of this trimetallic system and will build three-dimensional model for the activity function of these catalysts and also will be capable of evaluating some physical properties of these metals.

2. Experimental

2.1. Materials Used. NaOH (Merck), copper nitrate (Merck), nickel nitrate (Merck), silver(I) nitrate (Merck), hydrazine hydrate (99.999% Merck), alumina (FLUKA Typ 507c), Pnitrophenol (PNP) (Merck), o-nitrophenol (oNP) (Merck), m-nitrophenol (mNP) (Merck), P-aminophenol (PAP) (Merck), m-aminophenol (mAP) (Merck), and o-aminophenol (oAP) (Merck) were used as a standard materials.

2.2. Preparation of the Catalyst. Typically 10 g of alumina was impregnated with 5 wt% metals. Different mole ratios of mono-, di-, and trimetal are varied keeping 5wt% constant. After drying at 100[degrees]C the catalyst is subjected to chemical reduction using hydrazine hydrate in alkaline solution of NaOH. After completion of reduction, the catalyst was rapidly filtered and dried and kept in a closed bottle.

2.3. Catalytic Reaction. Typically, a solution containing 0.125 g of nitrophenols with 20 mL of hydrazine hydrate was heated to 80-100[degrees]C in a three-necked flask connected to a condenser.

0.5 g of the catalyst was added to the above solution. The time was recorded just upon the addition. After reaction completion the color of the system is changed to grayish white indicating 100% conversion [14]. The filtrate was then evaporated under reduced pressure. The residual solids were recrystallized from hot water to give the pure product of corresponding amino phenols in almost 100% yield.

2.4. Characterization Techniques

2.4.1. XRD (X-Ray Diffraction Analysis). X-Ray diffractograms of various solids were collected using a Bruker D8 advance instrument with CuK[alpha]1 target with second monochromator 40 kV, 40 mA.

2.4.2. EPR (Electron Paramagnetic Resonance). The EPR spectra were recorded on EMX Bruker instrument operated at X-band frequency. The following parameters are generalized to all samples otherwise mentioned in the text. Microwave frequency is 9.79 GHz. Receiver gain is 20. Sweep width is 6000, center at 3480 Gs. Microwave power is 0.202637 W.

2.4.3. Pulsed Chemisorption. The H2 chemisorption experiments were carried out at 373 K using a pulse reactor to determine the Ni metal area and Ni metal particle size. In a typical experiment, approximately 150 mg of the catalyst sample was loaded in a micro quartz reactor (8 mm i.d., and 250 mm long) and the catalyst sample was first subject to hydrogen flow at 420 K for 1 h and kept at the same temperature for 1 h under He flow and then the reactor was cooled to 373 K under helium gas flow. The outlet of the reactor was connected to a microthermal conductivity detector (TCD) of GC-17A (Quantachrome ChemBET 3000, USA) through an automatic six-port valve after cooling of the sample to 303 K, pulses of gas (5% H2 balance He) (500 mL), until there is no further change in the intensity of TCD peak due to gas pulse.

3. Results and Discussion

3.1. X-Ray Diffraction (XRD). Figure 1 represents the XRD patterns of bare alumina, 5% Ni, and some trimetallic systems. From these figures it could be shown that Ni metal phase was observed only in pure 5% wt Ni. While in the rest of the samples there was no observation of such phase. This could be explained by the lower amount of metal which could not be detected by XRD techniques. Another reason is that the metal phases could be existing in amorphous nanoscale with bi- or trimetallic system. This will be declared further in EPR section.

3.2. Electron Spin Resonance (EPR). EPR spectra of all samples are given in Figure 2. In this figure we can observe an EPR signal characterized for the nanosized nickel [13].

3.3. Program for Trimetallic System. In this research we aimed to study and evaluate trimetallic system of Ni, Cu, and Ag as an effective catalyst for hydrogenation of nitrophenols.

In order to study this system we make a series of bimetallic systems Ni:Cu and Ni:Ag with different molar ratios (Table 1). The catalytic activity was taken as time to reach 100% conversion [13]. However we added a term "catalytic activity response" as a reciprocal of this time. This was taken as real measure of catalytic activity and thus as time decreases catalytic activity response increases.

From experimental test it was found that neither Cu nor Ag alone gives any catalytic activity in these reactions; however in presence of Ni as a bimetallic system they could enhance the catalytic activity.

In order to study the effect of these metals on the activity of Ni, we first determined what is called the linear catalytic activity which is the catalytic activity of catalyst based on its % nickel theoretically calculated from the pure nickel catalyst. Based on these values we can check any presence of synergism occurring due to addition of either Cu or Ag as bimetallic system with nickel. A function of synergism was evaluated for bimetallic system individually (Ni:Cu and Ni:Ag), was given below, and was fitted with regression with [R.sup.2] more than 0.99 as indicated below (Figures 3 and 4).

Fitted Function of Ag

R2 = 0.99999.

y = (a + cx + ex2 + gx 3 + ix 4 + kx 5 + mx6 + ox7 + qx 8 + sx9)/(1 + bx + dx 2 + fx3 + hx 4 + jx5 + 1x6 + nx 7 + px 8 + rx9)

a = 8.38079978776094534e - 12.

b = -0.13125008769893421.

c = 0.00875045445894009892.

d = 0.00879799437475077272.

e = -0.000542659485512226170037.

f = -0.000369150693507672097.

g = 0.000130160541802780922.

h = 1.04721425663883469e - 05.

i = -2.37748383168755742e - 06.

j = -2.04370666255700862e - 07.

k = -1.04465938816921968e - 07.

I = 2.7069883330420037e - 09.

m = 4.38513923648865887e - 09.

n = -2.30678157052159122e - 11.

o = -6.44850744978172715e - 11.

p = 1.12348816431769573e - 13.

q = 4.3709878480847383e - 13.

r = -2.33307317855799149e - 16.

s = -1.15082085584729222e - 15.

where x is wt% of Ag in the sample and y is % syn/Ni.

Simulated Function of Cu Synergism

R2 = 0.9997.

y = (a+cx^(0.5)+ex+^xA(1.5)+ix^2)/(1+kx^(0.5) + dx + fx^(1.5) +hx^2)[NL]

a = -0.0426081493584968437.

b = -0.54328913086813246.

c = 0.0447085498764833328.

d = 0.108691551874143843.

e = 0.000882635994217492438.

f = -0.00934404638076721272.

g = -0.00135640497689789237.

h = 0.000291267840703249792.

i = 8.63726742343394856e - 05.

where x is wt% of Cu in the sample and y is % syn/Ni.

From Figures 3 and 4 curves it was found that the synergism function is increased as the % added metal (Cu or Ag) increases reaching maximum and then decreases again.

In order to study the trimetallic system we make a linear addition of both functions of individual synergism. Figure 5 represents the 3D graph of raw data given.

The above data was simulated as 3D function as given below:

z = a + b exp (- exp (-(x - c)/d) - (x - c)/d + 1) + e exp (- exp (-(y - f)/#) - (y - f)/# + 1) + h exp (- exp (-(x - c)/d) - (x - c)/d + 1) * exp (- exp (-(y - f)/#) - (y - f)/g + 1).

a = 1.06593487136815043.

b = 6.21497398634458147.

c = 30.766242892928571.

d = 10.6485929178985698.

e = 14.6057695738211414.

f = 36.2251355611607967.

g = 12.5973938666555902.

h = 0.371621313243641629.

R2 = 0.99606799,

where x is % copper, y is the % Ag, and z is the % syn/Ni.

Figure 6 represents the 3D model of simulated function which gives us high accuracy.

Figures 5 and 6 showed clearly that the 3D model of the linear synergism functions showed more than 3D peaks varied according to the composition of the system. The maximum synergism was found to be of value about 22% syn/Ni.

This 3D figure could give us the ability to evaluate the four parameters in one time (% syn, % Ni, % Cu, and % Ag). However, subsequently, analysis of the real system should be compared which will be performed in the next section.

After applying the previous function on real trimetallic systems we observed that extra synergism occurs due to presence of both Cu and Ag together. In order to evaluate this extra synergism we correlate the difference in synergism with the % Ni (Figure 7).

Thus, it was found that extra synergism is observed only in % Ni between 5 and 40%. In order to calculate it automatically we simulate this function as follows:

y = (a + c ln x + e(ln x)^2 + #(ln x)^3)/(1 + b ln x + d(ln x)^a2 + /(ln x)^3 + h(ln x)^4)

[R.sup.2] = 0.998.

a = 0.0635566682938822554.

b = -1.45700051352569521.

c = 0.0405819231287318062.

d = 0.798911010088653167.

e = -0.052037125263925555.

f = -0.195314109600566023.

g = 0.0106381602099602297.

h = 0.0179571310856602618.

where y is difference between simulated linear synergism and real trimetallic synergism and x is % Ni.

After applying the above function on the three-dimensional linear synergism function we could obtain the real function of synergism (Figure 8).

Obtaining the previous function enables us to deduce the catalytic activity and consequently the time to reach 100% for trimetallic system simply by input of the mole ratio of Ni:Cu:Ag.

Particle Size Simulation. Particle size was evaluated by Kawabata equation correlating the peak-to-peak width of EPR spectra of nanoparticles with corresponding particle size:

d = a * [square root] [DELTA][H.sub.pp],

where a is proportionality constant and [DELTA][H.sub.pp] is the peak width. Knowing that "a" for Ni is 1.6 [13] we can evaluate the particle size of each catalyst.

We correlate the particle size of different ratio of trimetallic catalysts with the function of real synergism Figure 9.

The function correlating the syn/Ni with particle size is as follows:

Eqn = Decay 1 + 2(fl, fc, c, d, e).

y = fl + fc exp(-cx) + d/(1 + dex).

y = -34.6564331294717461 + 6.41868775476660539* exp(-2.1574343708473217 * %) + 50.9940759663696104 / (1 + 50.9940759663696104 * 4.04301775665067334e 05 * %)

a = -34.6564331294717461,

b = 6.41868775476660539,

c = 2.1574343708473217,

d = 50.9940759663696104,

e = 4.04301775665067334e - 05,

[R.sup.2] = 0.9952975.

where y is particle size by nm and x is the syn/Ni.

By the above function we can deduce the particle size of any trimetallic system by the syn/Ni function.

In order to evaluate the secret of catalytic activity we make pulsed chemisorption to measure the metallic surface area and degree of dispersion and average crystallite size of Ni. This pulsed chemisorption was performed at reaction temperature (Table 2).

Correlating surface area per unite % Ni with the synergism function we can obtain a good correlation as in Figure 10.

We can simulate the previous function as follows:

y = fl + fc * exp(- exp(-((x - dln(ln(2)) - c)/d))).

r2 = 0.999964110919114507.

a = 0.0132405008193570401,

b = 0.381497786254137327,

c = 5.72848339592924586,

d = 1.48550214791616277,

where y is the metallic surface area by % Ni and x is the synergism function per % Ni.

By the above correlation we can simulate the metallic surface area to the synergism function easily to fully simulate the trimetallic system. The program written in Excel could simulate easily with a good precision the whole system for the all isomers of nitrophenol (p-, m-, and o-).

Figure 11 is the image of this Excel program which is attached with this manuscript as Supplementary Material (available online at https://doi.org/10.1155/2017/9464209).

Evaluation of the Program. In order to evaluate the program the catalytic activities of some random samples were measured and compared with data given from the program, Table 3.

From Table 3 we could realize that the program could predict precisely the time to reach 100% with average % error not exceeding 1.83% and max error not increasing by 8%.

Mechanism of Reduction of Nitrophenols. Figure 12 represents the kinetic curve of the three nitrophenols which shows that all reduction processes follow first-order equation with respect to nitrophenols.

Durability Study of Some Samples Given. From Table 4 it was found that most of trimetallic system showed a good durability upon five times of successive use.

4. Conclusions

The trimetallic system (Ni, Cu, and Ag) was proved to be very effective for reduction of nitrophenols using hydrazine hydrate. Thus, nickel metal was found to be the only active center in this reaction. However, the presence of bimetallic and trimetallic alloy with nickel exhibits extra synergism. A program with high precision was successfully written to simulate the synergism function and the catalytic activity of the trimetallic system. The method of calculation used will open new aspect to deal with similar system in the future. Some physical properties such as particle size and metallic surface area could be simulated successfully for whole trimetallic system.

https://doi.org/10.1155/2017/9464209

Conflicts of Interest

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

This project was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, under Grant no. 392/130/1436. The authors, therefore, acknowledge with thanks DSR technical and financial support. The authors would like also to acknowledge King Fahd Medical Center for the support in measuring the ESR samples.

References

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Salem M. Bawaked, (1) Islam Hamdy Abd El Maksod, (1,2) and Abdulmohsen Alshehri (1)

(1) Faculty of Science, Department of Chemistry, King Abdulaziz University, Jeddah, Saudi Arabia

(2) National Research Centre, Physical Chemistry Department, Dokki, Cairo, Egypt

Correspondence should be addressed to Islam Hamdy Abd El Maksod; islam_9000@yahoo.com

Received 4 December 2016; Revised 5 January 2017; Accepted 16 February 2017; Published 13 March 2017

Academic Editor: Mohamed Bououdina

Caption: FIGURE 1: XRD patterns of pure Ni, some trimetallic systems, and bare alumina.

Caption: Figure 2: EPR spectra of different investigated samples.

Caption: FIGURE 3: Fitted function of synergism of Ag.

Caption: FIGURE 4: Fitted function of synergism of Cu.

Caption: FIGURE 5: 3D presentation of trimetallic system Ni:Cu:Ag. Cu:Ag against synergism per % Ni.

Caption: FIGURE 6: 3D model for the trimetallic system of Ni:Cu:Ag.

Caption: FIGURE 7: Difference between real and linear synergism against % Ni.

Caption: FIGURE 8: 3D representation of calculated real synergism function.

Caption: FIGURE 9: Correlation between particle size and function of synergism over % Ni.

Caption: FIGURE 10: Metallic surface area per % Ni against synergism per % Ni.

Caption: FIGURE 11: Image of Excel program.

Caption: FIGURE 12: Kinetic curve of reaction of nitrophenols into aminophenol under our reaction conditions.
Table 1: Examples of some measured bimetallic and trimetallic
systems.

Catalyst (5 wt%       Time to reach 100% conversion (sec)
loading on alumina)
                         PNP          MNP          ONP

Ni                       505          149           80
1Ni:1Cu                  426           67          125
2Ni:1Cu                  145           23           43
1Ni:2Cu                  669          106          197
1Ni:1Ag                  403           64          119
1Ni:2Ag                  603           96          178
2Ni:1Ag                  136           22           40
1Ni:1Cu:1Ag              275           44           81
1Ni:2Cu:1Ag              300           47           89
1Ni:1Cu:2Ag              327           52           96
2Ni:1Cu:1Ag              138           22           41
2Ni:1Cu:2Ag              320           52           95
2Ni:2Cu:1Ag              179           29           53

Table 2: Experimental data for some selected samples for
dispersion and metallic surface area.

Catalyst      % Ni    Dispersion   Metal surface area

1Ni:1Ag:1Cu   25.65     30.41            10.13
2Ni:1Cu       64.9      55.27            18.42
1Ni:1Ag       35.43     32.51            10.83
Ni             100       4.12             1.37
2Ni:1Ag       52.32      3.63             1.21
1Ni:1Cu       48.04      2.71             0.9

Table 3: A comparison between real and calculated results of
some random samples combined with % error.

Catalyst         Time to reach 100% conversion (sec)
(5 wt% loading             PNP
on alumina)      Real   Calculated   % error

Ni               505      505.1       0.02
1Ni:1Cu          426      425.5       0.12
2Ni:1Cu          145      144.9       0.07
1Ni:2Cu          669      668.3       0.10
1Ni:1Ag          403      403.1       0.02
1Ni:2Ag          603      603.3       0.05
2Ni:1Ag          136      135.7       0.22
1Ni:1Cu:1Ag      275      274.7       0.11
1Ni:2Cu:1Ag      300      299.1       0.30
1Ni:1Cu:2Ag      327      327.2       0.06
2Ni:1Cu:1Ag      138      137.3       0.51
2Ni:1Cu:2Ag      320      319.6       0.12
2Ni:2Cu:1Ag      179      178.3       0.39
4Ni:1Cu:2Ag      140      138.2       1.29
1Ni:2Cu:3Ag      1128      1122       0.53
3Ni:1Cu:1Ni      104       105        0.96
1Ni:3Cu:2Ag      718      716.8       0.17
2Ni:1Cu:2Ag      322      319.6       0.75
Average error                         0.32

Catalyst         Time to reach 100% conversion (sec)
(5 wt% loading             MNP
on alumina)      Real   Calculated   % error

Ni               149      148.7       0.20
1Ni:1Cu           67      67.27       0.40
2Ni:1Cu           23       22.9       0.43
1Ni:2Cu          106      105.7       0.28
1Ni:1Ag           64      63.72       0.44
1Ni:2Ag           96      95.39       0.64
2Ni:1Ag           22      21.45       2.50
1Ni:1Cu:1Ag       44      43.42       1.32
1Ni:2Cu:1Ag       47      47.29       0.62
1Ni:1Cu:2Ag       52      51.73       0.52
2Ni:1Cu:1Ag       22      21.71       1.32
2Ni:1Cu:2Ag       52      50.53       2.83
2Ni:2Cu:1Ag       29      28.19       2.79
4Ni:1Cu:2Ag       23      21.84       5.04
1Ni:2Cu:3Ag      180      177.3       1.50
3Ni:1Cu:1Ni       18       16.6       7.78
1Ni:3Cu:2Ag      115      113.3       1.48
2Ni:1Cu:2Ag       52      50.53       2.83
Average error                         1.83

Catalyst         Time to reach 100% conversion (sec)
(5 wt% loading             ONP
on alumina)      Real   Calculated   % error

Ni                80      79.86       0.18
1Ni:1Cu          125      125.3       0.24
2Ni:1Cu           43      42.66       0.79
1Ni:2Cu          197      196.8       0.10
1Ni:1Ag          119      118.7       0.25
1Ni:2Ag          178      177.7       0.17
2Ni:1Ag           40      39.95       0.12
1Ni:1Cu:1Ag       81      80.88       0.15
1Ni:2Cu:1Ag       89      88.08       1.03
1Ni:1Cu:2Ag       96      96.35       0.36
2Ni:1Cu:1Ag       41      40.43       1.39
2Ni:1Cu:2Ag       95      94.11       0.94
2Ni:2Cu:1Ag       53      52.51       0.92
4Ni:1Cu:2Ag       42      40.68       3.14
1Ni:2Cu:3Ag      333      330.3       0.81
3Ni:1Cu:1Ni       32      30.92       3.37
1Ni:3Cu:2Ag      213      211.1       0.89
2Ni:1Cu:2Ag       96      94.11       1.97
Average error                         0.94

Table 4: A durability study for some trimetallic
samples for reduction of PNP.

Sample                Time to reach 100% for PNP (sec)
              1st use   2nd use   3rd use   4th use   5th use

1Ni:1Cu:1Ag     275       280       290       300       330
1Ni:2Cu:1Ag     300       310       310       330       350
1Ni:1Cu:2Ag     327       328       330       335       340
2Ni:1Cu:1Ag     138       140       142       146       150
2Ni:1Cu:2Ag     320       322       324       330       340
2Ni:2Cu:1Ag     179       182       183       185       190
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Title Annotation:Research Article
Author:Bawaked, Salem M.; Maksod, Islam Hamdy Abd El; Alshehri, Abdulmohsen
Publication:Journal of Nanomaterials
Article Type:Case study
Date:Jan 1, 2017
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