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Original article
11 (
6
); 991-999
doi:
10.1016/j.arabjc.2018.03.023

Hierarchical nanocrystalline NiO with coral-like structure derived from nickel galactarate dihydrate: An active mesoporous catalyst for methyl ethyl ketone production

, ,
 Chemistry Department, Faculty of Science at Qena, South Valley University, Qena 83523, Egypt

⁎Corresponding author. Samih.halawy11@gmail.com (Samih A. Halawy)

Received: , Accepted: ,
© The Author(s) 2018
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Nanocrystalline NiO with a coral-like structure (38 nm) has been prepared via thermal decomposition of a new precursor, nickel galactarate (NiC6H8O8·2H2O), at 500 °C for 3 h in air. Thermal decomposition of that precursor was studied by TG and DSC techniques. The resultant NiO was physicochemically characterized by XRD, FTIR, SEM, surface area, porosity and CO2-TPD. NiO was found to exhibit a remarkable activity towards the synthesis of MEK from 2-butanol between 200 and 325 °C. In addition, it has shown a great tendency to ease regeneration of the used catalyst after 192 h in stream by simple refreshing method.

Keywords

2-Butanol
Characterizations
Catalysis
Nickel galactarate
Nanocrystalline
Methyl ethyl ketone
1

1 Introduction

Design of hierarchical nanocrystalline metal oxides with special structure is of crucial interest, due to their diverse applicability in a range of areas. Nanocrystalline NiO, as a transition metal oxide, is considered as a promising material for its potential applications in topics, such as: waste-water treatment (Zheng et al., 2017; Zhao et al., 2015), photocatalysis (Fazlali et al., 2015), catalysis (Bonomo et al., 2017; Younas et al., 2016; Ye et al., 2016; Gajengi et al., 2015), gas sensors (Li, 2017; Khalaf et al., 2017), as anode material for Li-ion batteries (Li et al., 2017; Mollamahale et al., 2017) and as antibacterial and anti-inflammatory material in biomedicine (Ezhilarasi et al., 2016; Shanaj and John, 2016). Numerous experimental methods have been applied for the preparation of NiO, with different morphologies, from various precursors including: NiO nanowires (Li, 2017), nanoflakes (Suresh et al., 2017), nanorods and nanocubes (Bai et al., 2013), flowerlike porous hollow nanostructures (Feng et al., 2016), ultrathin nanosheets (Yao et al., 2015) and hollow microspheres (Li et al., 2017). Previously we have reported the thermal decomposition of another nickel carboxylate salt, in different atmospheres, such as nickel oxalate dihydrate (Mohamed et al., 2005). A major interest of our research group, at the moment, is directed towards exploring the morphology, structure and catalytic activity of metal oxides that are prepared from new and traceless precursors like metal galactarates. We have recently reported the preparation of nanocrystalline MgO using magnesium galactarate hemihydrate MgC6H8O8·0.5H2O, with high surface area and strong basic properties (El-Nahas et al., 2017).

Methyl ethyl ketone (MEK) is used as a multi-purpose solvent, in surface coatings, removal of paints and varnish, printing inks, and as an extraction medium for oils, fats, resins and waxes (A.M.T.H., 2014). Also, MEK has potential applications as a fuel substitute (Thion et al., 2017; Hoppe et al., 2016) and as a catalyst for polyester resins hardening (Al-Sunbul et al., 2016).

The main objective of this study is to provide an easy method to prepare hierarchically nanocrystalline NiO, with a characteristic morphology, in a short time using a novel and non-toxic precursor nickel galactarate dihydrate, NiC6H8O8·2H2O. Also, the obtained NiO was physicochemically characterized and was tested for the catalytic activity for the synthesis of MEK from 2-butanol.

2

2 Material and methods

2.1

2.1 Preparation of the precursor

The home-made crystalline nickel galactarate was prepared as the recently published method (El-Nahas et al., 2017). Briefly, a calculated amount of galactaric acid (C6H10O8, Merck) was dissolved in 100 mL of deionized water at 70 °C. Nickel basic carbonate hydrate powder [NiCO3·2Ni(OH)2·xH2O] was slowly added with continuous stirring, until there was no further CO2 released, indicating the complete reaction between the two reactants. This results in the formation of a pale green precipitate of Ni-Galactarate, which was then washed several times with deionized water, and was then dried in an oven at 100 °C overnight. Then the resultant solid was calcined at 500 °C in static air for 3 h in a muffle furnace.

2.2

2.2 Characterization methods

Numerous bulk and surface investigation methods have been used in order to characterize both the precursor and the final oxide (NiO).

2.2.1

2.2.1 Bulk characterization

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed at a heating rate of 3 °C/min in a stream of dry nitrogen flowing at 40 mL/min, using a 50H Shimadzu thermal analyzer (Japan). The thermal analyzer is equipped with a data acquisition and handling system (TA-50WSI). Highly sintered α–Al2O3 was used as the reference material in DSC measurements, while temperature and enthalpy readings were calibrated versus the melting point, i.e. 156.3 °C (Lide, 2004) and the heat of fusion, ΔHf = 28.24 J/g (Lide, 2004) of Specpure Indium metal (a Johnson Matthey product), respectively. Elemental analysis was carried out using Perkin Elmer 2400 Series II CHNS/O analyzer.

Samples of the Ni-Galactarate precursor and NiO were analyzed by X-ray powder diffraction (XRD) method using a Brucker AXS-D8 Advance diffractometer (Germany), equipped with a copper anode generating Ni-filtered CuKα radiation (λ = 1.5406 Å), in the 2θ range between 10°-80°, supported with interfaces of DIFFRACplus SEARCH and DIFFRACplus EVA to facilitate an automatic search and match of the crystalline phases for identification purposes with ICDD data base.

The FTIR spectra were recorded using a Magna-FTIR 500 (USA), between 4000 and 400 cm−1, operating a Nicolet Omnic software and adopting the KBr disk technique.

The Scanning Electron Microscopic study, SEM, of NiO sample was carried out using a FEI Quanta environmental SEM Oxford Ex-ACT using XT microscope Control software.

2.2.2

2.2.2 Surface characterization

The surface textural properties of NiO sample that has been calcined at 500 °C (viz. specific surface area, pore volume and mean pore radius) were determined from nitrogen adsorption-desorption isotherms recorded at liquid nitrogen temperature, −196 °C, using an automatic Micromeritics ASAP 2010 (USA), equipped with an online data acquisition and handling system operating BET and BJH analytical software for the adsorption-desorption data, assuming a cylindrical pore model (Sing et al., 1985). The measured sample was degassed at 200 °C and 10−5 Torr for 2 h before measurement (1 Torr = 133.3 Pa).

The surface basicity/basic sites strength distribution over NiO sample was investigated by temperature-programmed desorption of CO2 (CO2-TPD). NiO sample (≅100 mg) was initially heated at 450 °C for 1 h in air, then was immediately transferred into a Pyrex-glass chamber fitted with inlet/outlet allowing for a CO2-stream (100 mL/min) to pass at room temperature. After 48 h, ≅20 mg of the CO2-covered sample were subjected to DSC analysis using 40 mL/min as N2-flow with 20 °C/min heating rate.

2.3

2.3 Catalytic activity measurements

Catalytic activity and selectivity of NiO for the conversion of 2-butanol (2BA) to 2-butanone, methyl ethyl ketone (MEK), in the temperature range of 200–325 °C were investigated. For each test, 0.2 g of catalyst was preheated at 400 °C inside a continuous-flow fixed bed reactor for 1 h in N2-flow before measurements, then the temperature was lowered gradually to 200 °C. Two values of gas hourly space velocity (GHSV) i.e. 12,000 and 24,000 mL gcat−1 h−1 were used. The carrier gas (N2) was passed through a bubbler containing liquid 2BA (Fluka, ≥99%) held at 0 °C. The temperature in the experiment was varied stepwise from 200 to 325 °C. The alcohol vapours in N2-feed flow were adjusted using mass flow controller Shimadzu FC-40. The reactor effluent was analyzed by a (Shimadzu GC-14) gas chromatograph, equipped with a data processor model Shimadzu Chromatopac C-R4AD. Automatic sampling was continuously performed using a heated gas sampling cock, type HGS-2 at 140 °C, using (FID) flame ionization detector and a stainless steel column (PEG 20 M 20% on Chrmosorb W, 60/80 mesh, 3 m × 3 mm) at 80 °C. The retention time of 2BA and the expected products has been calibrated, in separate experiments, using pure samples.

3

3 Results and discussion

3.1

3.1 Thermal analyses

In order to study the thermal decomposition steps of the prepared NiC6H8O8·2H2O, both TGA and DSC were carried out, at a relatively slow heating rate (i.e. 3 °C/min). Fig. 1 shows the TGA curve which displays a group of successive steps ascribed to the dehydration and the decomposition steps. The decomposition is shown to be completed at ≤500 °C, with a total mass loss (ML) of 75.3% of the original sample weight. This value of ML is very close to that expected to result from the production of NiO as a final solid product (i.e. 75.33%). The DSC curve in Fig. 1 displays two main endothermic peaks with Tmax values at 112 and 172 °C, both peaks are ascribed to dehydration steps, followed by another two endothermic peaks maximized at Tmax of 311 and 342 °C, corresponding to the decomposition of anhydrous Ni-galactarate to give NiO. From the thermal analyses, one can conclude that calcination of the precursor NiC6H8O8·2H2O at 500 °C, for 3 h in a static air, is sufficient to produce well defined NiO.

TG and DSC curves of nickel galactarate dihydrate, NiC6H8O8·2H2O, carried out at a heating rate of 3 °C/min in a flow rate of dry N2 (40 mL/min).
Fig. 1
TG and DSC curves of nickel galactarate dihydrate, NiC6H8O8·2H2O, carried out at a heating rate of 3 °C/min in a flow rate of dry N2 (40 mL/min).

3.2

3.2 Elemental analysis

Results of the elemental analysis of the original precursor NiC6H8O8·2H2O were as follows: % C = 23.85 while % H = 4.06. These results are in accordance with a dihydrate structure of the salt where the calculated theoretical values should be 23.79 and 3.99% for carbon and hydrogen content, respectively.

3.3

3.3 X-ray powder diffraction (XRD)

Fig. 2 illustrates the XRD patterns of the original precursor NiC6H8O8·2H2O, together with that of the final solid product produced. Diffractogram (a) of the parent salt exhibits some sharp reflections in the 2θ range of 5–35°. These sharp reflections are not present for the product (diffractogram (b)). The XRD diffractogram (b) of NiO is similar to that of rhombohedral NiO (ICDD, 44-1159). It displayed a group of very sharp reflections at 37.253° (1 1 1), 43.29° (2 0 0), 62.897° (2 2 0), 75.4° (3 1 1) and 79.469° (2 2 2) which belong to face centered system (ICDD, 44-1159). In addition, two very minor reflections attributed to metallic Ni (ICDD, 004-0850) appeared at 44.472° and 51.5°. The presence of traces of Ni metal in the solid residue may be due to reduction of a finite amount of NiO by carbon deposition during the decomposition step of the galactarate salt, as reported previously (Cheng et al., 2016):

(1)
2NiO + C → 2Ni + CO2
XRD diffractograms of (a) nickel galactarate dihydrate, NiC6H8O8·2H2O, as prepared and (b) NiO at 500 °C as final solid product.
Fig. 2
XRD diffractograms of (a) nickel galactarate dihydrate, NiC6H8O8·2H2O, as prepared and (b) NiO at 500 °C as final solid product.

Cao et al. (2006) suggested the direct reduction of CuO by coal char that could occur at 500 °C. Another mechanism has also been proposed (Cheng et al., 2016) for the reduction of NiO by the liberated reactive volatile carbonaceous material as follows:

(2)
CH0.6 + 2.3 NiO → 2.3Ni + CO2 + 0.3H2O

From the XRD results, the crystallite sizes of the prepared precursor and the corresponding NiO were estimated using the Debye-Scherrer equation (Cullity and Stock, 2001). The particle size of the NiC6H8O8·2H2O precursor was calculated as 56.2–59.1 nm, while the produced NiO was in the range 37.9–38.0 nm. These results give an insight that nickel galactarate is a suitable precursor for the production of nanocrystalline NiO. Our results showed that the particle size of NiO are in agreement with previously published results on the synthesis and characterization of NiO nanoparticles (El-Kemary et al., 2013; Dharmaraj et al., 2006).

3.4

3.4 FT-IR spectroscopy analysis

The FT-IR spectroscopy has been used to identify the different reactive groups of the prepared precursor and the corresponding NiO at 500 °C. Fig. 3 reports the IR spectra of galactaric acid (a), parent nickel galactarate (b) together with spectrum of the resulted NiO (c) after decomposition at 500 °C. Spectrum (a) of pure galactaric acid displays all the absorption bands, centered at the same wave numbers, as previously published (Tian et al., 2000). Spectrum (b) of the prepared NiC6H8O8·2H2O shows the stretching vibrations (νOH) centered at 3350 and 3200 cm−1, while the band at 3410 cm−1 is attributed to the vibration of water of hydration (Tian et al., 2000). Some weak bands appeared in the region 2958–2660 cm−1 that may be assigned to C—H vibrations of aliphatic chain (Pajtášová et al., 2010). A very strong peak at 1724 cm−1 was assigned to C⚌O stretching vibration (νC⚌O) of galactaric acid, as shown in spectrum (a), which was shifted towards lower frequency and has been split into two bands at 1600 and 1434 cm−1, which is reported to occur as a result of the coordination of the galactarate anions with Ni2+ (Tian et al., 2000). These two absorption bands in spectrum (b) of Ni-galactarate are attributed to asymmetric and symmetric stretching vibrations (denoted as νas and νs) of the anion COO− groups, respectively. Spectrum (b), also, displayed a group of absorption bands appeared in the range of 1389–1213 cm−1 attributed to the bending vibrations of C—O—H and C—C—H groups (Saladini et al., 2000). Strong and sharp stretching vibrations of the C—O groups are reported (Saladini et al., 2000; Tajmir-Riahi, 1990) to appear in the 1099–985 cm−1 region. The absorption bands between 846 and 421 cm−1 may belong to different assignments as follows: τOCCO, τOCCC and δCCO (Tian et al., 2000). In addition to the above mentioned bands, there are two sharp bands at 2361 and 2341 cm−1 which appeared in spectra (b & C) for νas of the adsorbed CO2 over the KBr disc (Busca and Lorenzelli, 1982). Finally, spectrum (c) of NiO produced by calcination of NiC6H8O8·2H2O at 500 °C, showed a sharp and strong stretching vibration mode at 433 cm−1 of pure NiO nanocrystals (Derikvandi and Nezamzadeh-Ejhieh, 2017; El-Kemary et al., 2013).

FT-IR spectra of (a) pure galactaric acid, (b) nickel galactarate dihydrate, and (c) NiO at 500 °C.
Fig. 3
FT-IR spectra of (a) pure galactaric acid, (b) nickel galactarate dihydrate, and (c) NiO at 500 °C.

3.5

3.5 Morphology of NiO catalyst

The morphologies of the obtained NiO was investigated using SEM. Fig. 4 shows SEM images of NiO at different magnification values. These images report porous coral-like nanostructures. In order to acquire further information about the nanostructure of NiO, Fig. 4b–d, shows higher magnifications of the selected area. Clearly, these images show hierarchical units that are connected together to form coral-like nanostructures. These units, also, seem to be composed of series of dendrite-like aggregates.

SEM images of the product NiO at 500 °C: (a) general image, (b–d) high magnifications of selected areas of NiO.
Fig. 4
SEM images of the product NiO at 500 °C: (a) general image, (b–d) high magnifications of selected areas of NiO.

3.6

3.6 Surface area and porosity measurements

BET surface area and pore-size distribution are considered as very important factors in the field of catalysis, therefore, specific surface area and pore-size distribution of the NiO were determined using N2 adsorption-desorption isotherm, as shown in Fig. 5(A). It is classified as a type IV isotherm with H3-type hysteresis loop (P/P° > 0.4), that indicates the existence of a number of mesopore structures (Sing et al., 1985). Fig. 5(B) reports the corresponding pore size distributions that were calculated by Barrett-Joyner-Halenda (BJH) method from the desorption branch. It is clear that the majority of pore size are in the range 3.4 and 5.0 nm, with a few pores larger than 30 nm, suggesting the evident characteristics of hierarchical mesoporous nature of NiO (Yao et al., 2015). However, the BET surface area of NiO produced by calcination of NiC6H8O8·2H2O at 500 °C, for 3 h, was calculated to be 5.02 m2/g. The abundant mesopores and hierarchical structure of NiO would facilitate the effective contact of active sites over the catalyst surface and mass transport during the catalytic reaction that will be discussed later.

N2 adsorption/desorption isotherm (A) and BJH pore diameter curve (B) of NiO at 500 °C, that obtained by calcination of NiC6H8O8·2H2O for 3 h in air.
Fig. 5
N2 adsorption/desorption isotherm (A) and BJH pore diameter curve (B) of NiO at 500 °C, that obtained by calcination of NiC6H8O8·2H2O for 3 h in air.

3.7

3.7 Catalytic conversion of 2-butanol (2BA)

The catalytic activity of the prepared NiO at 500 °C, from NiC6H8O8·2H2O, was examined during the gas phase conversion of 2BA. The reaction was studied chromatographically inside a flow reactor, under atmospheric pressure, using GHSV = 12,000 mL gcat−1 h−1 while the reaction temperature was varied stepwise from 200 to 325 °C. The results are presented in Fig. 6A. As the temperature increased the catalyst activity is significantly improved, where% conversion steadily increased from 23.27% (at 200 °C) up to 96.07% (at 325 °C). The major product of 2BA conversion was methyl ethyl ketone (MEK), and its% selectivity was found to be inversely proportional to reaction temperature in the range 96.2–92.5%. On the other hand, both trans-2-butene (t-2-C4H8) and cis-2-butene (c-2-C4H8) have been detected as minor products with total % selectivity not exceeding 3% until a reaction temperature of 275 °C. Above 275 °C, % selectivity of t-2-C4H8 was increased to be double its value. There is also an unknown product with % selectivity ≤2.8% which was detected by GC after unreacted 2BA.

Activity of NiO catalyst during the conversion of 2-butanol (2BA) to its products (A) using GHSV = 12,000 mL gcat−1 h−1, and (B) with GHSV = 12,000 & 24,000 mL gcat−1 h−1 focusing on the main product, as a function of reaction temperature.
Fig. 6
Activity of NiO catalyst during the conversion of 2-butanol (2BA) to its products (A) using GHSV = 12,000 mL gcat−1 h−1, and (B) with GHSV = 12,000 & 24,000 mL gcat−1 h−1 focusing on the main product, as a function of reaction temperature.

These results revealed that the catalyst has prevailing basic characters since it is mainly active in the dehydrogenation reaction of 2BA as concluded previously, especially when N2 is used as carrier gas (Cheikhi et al., 2005; Perez-Lopez et al., 2005). In the dehydrogenation of 2BA, the basic sites essentially interfere in the abstraction of hydrogen from alcohols as previously proposed (Takarroumt et al., 2013; Khachani et al., 2010).

On the other hand, the presence of limited population of the acidic sites have led to the production of butenes as minor products, with less than 7% selectivity. In order to study the effect of space velocity on the catalyst reactivity during conversion of 2BA, in the temperature range, 200–325 °C, two GHSV values namely 12,000 and 24,000 mL gcat−1 h−1 were used. From the presented results in Fig. 6B, it is observable that increasing of the space velocity was accompanied by a significant decrease in % conversion of 2BA at all applied reaction temperatures. This phenomenon meant that at a higher value of GHSV insufficient time was allowed for 2BA gas molecules to react. On the other hand, % selectivity of MEK production has been very little influenced by changing GHSV value. This may be attributed to the fact that mesoporous basic catalysts, such as NiO as concluded from its porosity measurements Fig. 5B, are more favorable in the production of MEK exclusively. On the other hand, it was unfavorable for the production of other products (Fang et al., 2009).

In order to distinguish the different types of basic sites over NiO sample that prepared at 500 °C, for 3 h in air from NiC6H8O8·2H2O, CO2-TPD measurement was performed (see Fig. 7). Three peaks appeared at 170, 273 and 360 °C, confirming that NiO has several CO2 desorption sites, as follows: weak sites (peak at 170 °C) attributed to bicarbonate species, intermediate sites (peak at 273 °C) ascribed for bidentate carbonates desorbed from Mn+-O2− pairs, and finally strong basic sites (peak at 360 °C) that assigned to unidentate carbonates on O2− sites (Saad et al., 2017; León et al., 2010). From the CO2-TPD results of Fig. 7, it is noticeable that strong basic sites are the dominant sites over NiO surface. This can explain the high activity and selectivity towards the production of MEK, at all reaction temperatures, during the conversion of 2BA, as presented in Fig. 6, where high populations of strong basic sites are clearly favoured.

CO2-TPD profile of NiO at 500 °C.
Fig. 7
CO2-TPD profile of NiO at 500 °C.

To examine the durability and stability of NiO as a catalyst during the dehydrogenation of 2BA to MEK, an experiment was carried out using the same catalyst sample with a long time on stream (TOS) up to 192 h, where the optimized reaction conditions were chosen as: GHSV = 12,000 mL gcat−1 h−1 and reaction temperature at 250 °C. The catalyst activity, as shown in Fig. 8, was found to slightly decrease with time. After 48 h, the conversion has decreased by 2%, then the catalyst exhibited a remarkable stability for as long as 96 h under the operating conditions. % conversion remains in the range 53.71–53.33% between 48 and 96 h. After that, % conversion showed a steady and slight decrease to about 50%. The same behaviour can be shown in case of% selectivity of MEK production, where its value was decreased by about 10% along that time duration on stream. We attributed this minor deactivation of NiO catalyst to the deposition of carbon in the form of fine particles over the catalyst surface, as detected previously (Aouissi et al., 2012; Delsarte and Grange, 2004).

Effect of long TOS (192 h) on 2BA% conversion and% selectivity of MEK production at 250 °C, over 0.2 g NiO catalyst using GHSV = 12,000 mL gcat−1 h−1.
Fig. 8
Effect of long TOS (192 h) on 2BA% conversion and% selectivity of MEK production at 250 °C, over 0.2 g NiO catalyst using GHSV = 12,000 mL gcat−1 h−1.

These fine carbon particles may block a substantial amount of the strong basic sites that responsible for the conversion of 2BA to MEK. A small specimen (i.e. ≅ 5 mg) of the used catalyst after 192 h was subjected to temperature programmed oxidation (TPO) analysis, that was conducted by TGA to estimate the mass loss %, which is due to the oxidation of carbon that was deposited over NiO surface. A heating rate of 20 °C/min and a flow of pure O2-gas 40 mL/min were used between room temperature up to 490 °C. Fig. 9 shows TPO profile of a sample of used NiO, where the carbonaceous deposit was calculated to be 19.68%. These fine particles of carbon remain stable up to 320 °C, then vastly undergo oxidation in the form of CO2 leaving the NiO surface.

TPO profile of the used NiO catalyst, for 192 h on stream, upon heating at 20 °C/min in pure oxygen 40 mL/min.
Fig. 9
TPO profile of the used NiO catalyst, for 192 h on stream, upon heating at 20 °C/min in pure oxygen 40 mL/min.

It is worth-noting that phenomenon of coke formation on the catalyst surface, during dehydrogenation of 2BA to MEK, has been reported previously at temperatures higher than 300 °C (Skrdla and Lindemann, 2003; Keuler et al., 2001), where 2BA conversion has been hindered which agreed with our results. This is a possible factor of catalyst deactivation at higher temperatures for a long time in the stream. Furthermore, regeneration of the used catalyst after 192 h on a stream of 2BA was accomplished by passing air flow (50 mL/min) through the catalyst bed inside the reactor, with a heating rate of 10 °C/min until 475 °C. The catalyst was kept at 475 °C for 3 h to make assure that NiO catalyst becomes free from any carbonaceous residue, as concluded from the TPO profile (Fig. 9). Fig. 10 shows a catalytic activity test for that regenerated NiO (R-NiO) during the conversion of 2BA to MEK, in comparison with the results of the fresh catalyst (F-NiO), both were carried out at the same reaction conditions.

Comparison of the catalytic activity between fresh NiO (F-NiO) and the regenerated catalyst (R-NiO), after 192 h on stream, during the conversion of 2BA to MEK at a reaction temperature range of 200–325 °C, with GHSV = 12,000 mL gcat−1 h−1.
Fig. 10
Comparison of the catalytic activity between fresh NiO (F-NiO) and the regenerated catalyst (R-NiO), after 192 h on stream, during the conversion of 2BA to MEK at a reaction temperature range of 200–325 °C, with GHSV = 12,000 mL gcat−1 h−1.

Focusing on the calculated values of % conversion of 2BA and % selectivity of MEK as a major product, see Fig. 10, both R-NiO and F-NiO exhibited almost the same reactivity and selectivity during all reaction temperatures between 200 and 300 °C with GHSV = 12,000 mL gcat−1 h−1. At 325 °C, R-NiO had a decrease of % selectivity towards MEK production. This is important evidence that NiO, produced from NiC6H8O8·2H2O at 500 °C, can be regenerated by a simple procedure of exposing the used catalyst to air at temperatures <500 °C, see Fig. 10.

4

4 Conclusions

Hierarchically nanocrystalline NiO with coral-like structure (38 nm) was prepared by direct thermal decomposition of a new and non-toxic precursor NiC6H8O8·2H2O at 500 °C. SEM images of NiO showed porous coral-like nanostructure particles. BET surface area was calculated for NiO as 5.02 m2/g, with mesopores in the range of 3.4 and 5.0 nm, with few pores larger than 30 nm. NiO is a good catalyst for the decomposition of 2-butanol, showing activity towards MEK production (i.e.% SMEK > 92%) in reaction temperature range of 200–325 °C. This catalytic behavior was attributed to the variety of the distributions of the strong basic sites over the catalyst surface, as concluded from CO2-TPD results. The prepared catalyst, NiO, exhibited a significant catalytic durability and stability during the catalytic conversion of 2-butanol to MEK with long time (192 h) on stream. A simple recycling process of the used catalyst was applied, in situ, by passing air flow (50 mL/min) through the catalyst bed at 475 °C to regenerate the catalyst again. In conclusion, the current study has provided insights that NiC6H8O8·2H2O could be used as a suitable precursor for the preparation of hierarchically nanostructure NiO, with mesopores and variety of strong basic sites on its surface, as a good dehydrogenation catalyst for alcohols, specifically of 2-butanol in the reported case.

Acknowledgement

The authors gratefully acknowledge Prof. D.W. Roony and Dr. A.I. Osman, Queen's University, Belfast, for the SEM images taken. The authors also offer a sincere thank you to Dr. K. Morgan for his diligent proofreading of this paper.

Conflict of interest

The authors declare that no conflict of interest and declare that this research is not funded by any other division outside SVU.

References

  2. , , , . Surface and bulk properties of dental resin composites after solvent storage. Dent. Mater.. 2016;32:987-997.
    [Google Scholar]
  3. , , , . Conversion of isobutane in presence of carbon dioxide over molybdenum oxide catalysts obtained from heteropolymolybdate precursors. Chin. J. Catal.. 2012;33:1474-1479.
    [Google Scholar]
  4. , , , , , , , , . The microemulsion preparation and high catalytic performance of mesoporous NiO nanorods and nanocubes for toluene combustion. Chem. Eng. J.. 2013;219:200-208.
    [Google Scholar]
  5. , , , , , , , . Surface properties of nanostructured NiO undergoing electrochemical oxidation in 3 methoxy-propionitrile. Appl. Surf. Sci.. 2017;403:441-447.
    [Google Scholar]
  6. , , . Infrared spectroscopic identification of species arising from reactive adsorption of carbon oxides on metal oxide surfaces. Mater. Chem.. 1982;7:89-126.
    [Google Scholar]
  7. , , , . Investigation of chemical looping combustion by solid fuels. 2. Redox reaction kinetics and product characterization with coal, biomass, and solid waste as solid fuels and CuO as an oxygen carrier. Energy Fuels. 2006;20:1845-1854.
    [Google Scholar]
  8. , , , , , , , . Direct synthesis of methyl isobutyl ketone in gas-phase reaction over palladium loaded hydroxyapatite. J. Catal.. 2005;232:257-267.
    [Google Scholar]
  9. , , , . Temperature-programmed reduction of nickel steam reforming catalyst with glucose. Appl. Catal. A. 2016;527:1-8.
    [Google Scholar]
  10. , , . Elements of X-ray Diffraction (third ed.). Michigan: Prentice Hall Publisher; .
  11. , , . Butan-1-ol and butan-2-ol dehydration on nitrided aluminophosphates: influence of nitridation on reaction pathways. Appl. Catal. A. 2004;259:269-279.
    [Google Scholar]
  12. , , . Synergistic effect of p-n heterojunction, supporting and zeolite nanoparticles in enhanced photocatalytic activity of NiO and SnO2. J. Colloid Interface Sci.. 2017;490:314-327.
    [Google Scholar]
  13. , , , , , , . Synthesis of nickel oxide nanoparticles using nickel acetate and poly(vinyl acetate) precursor. Mater. Sci. Eng. B. 2006;128:111-114.
    [Google Scholar]
  14. , , , . Nickel oxide nanoparticles: Synthesis and spectral studies of interactions with glucose. Mater. Sci. Semicond. Proc.. 2013;16:1747-1752.
    [Google Scholar]
  15. , , , , . Nanocrystalline MgO samples (11.5 and 12.6 nm) derived from two different precursors: characterization and catalytic activity. J. Therm. Anal. Calorim.. 2017;129:1313-1322.
    [Google Scholar]
  16. , , , , , , . Green synthesis of NiO nanoparticles using Moringa oleifera extract and their biomedical applications: Cytotoxicity effect of nanoparticles against HT-29 cancer cells. J. Photochem. Photobiol. B Biol.. 2016;164:352-360.
    [Google Scholar]
  17. , , , , , , , , . Synthesis and applications of mesoporous Cu-Zn-Al2O3 catalyst for dehydrogenation of 2-butanol. J. Nat. Gas Chem.. 2009;18:179-182.
    [Google Scholar]
  18. , , , . A new route for synthesis of spherical NiO nanoparticles via emulsion nano-reactors with enhanced photocatalytic activity. Solid State Sci.. 2015;48:263-269.
    [Google Scholar]
  19. , , , , , . NiO Flowerlike porous hollow nanostructures with an enhanced interfacial storage capability for battery-to pseudocapacitor transition. Electrochim. Acta. 2016;222:1160-1168.
    [Google Scholar]
  20. , , , . NiO nanoparticles catalyzed three component coupling reaction of aldehyde, amine and terminal alkynes. Catal. Commun.. 2015;72:174-179.
    [Google Scholar]
  21. , , , , , , . Tailor-Made fuels from biomass: Potential of 2-butanone and 2-methylfuran in direct injection spark ignition engines. Fuel. 2016;167:106-117.
    [Google Scholar]
  22. , , , . The dehydrogenation of 2-butanol over copper-based catalysts: optimising catalyst composition and determining kinetic parameters. Appl. Catal. A. 2001;218:171-180.
    [Google Scholar]
  23. , , , , , , , . Iron–calcium–hydroxyapatite catalysts: Iron speciation and comparative performances in butan-2-ol conversion and propane oxidative dehydrogenation. Appl. Catal. A. 2010;388:113-123.
    [Google Scholar]
  24. , , , , . Influence of discharge voltage on the sensitivity of the resultant sputtered NiO thin films toward hydrogen gas. Phys. B. 2017;514:78-84.
    [Google Scholar]
  25. , , , , , , . Adsorption of CO2 on hydrotalcite-derived mixed oxides: sorption mechanisms and consequences for adsorption irreversibility. Ind. Eng. Chem. Res.. 2010;49:3663-3671.
    [Google Scholar]
  26. , , , , , , , , . Highly controlled synthesis of multi-shelled NiO hollow microspheres for enhanced lithium storage properties. Mater. Res. Bull.. 2017;87:224-229.
    [Google Scholar]
  27. , . Supersensitive and superselective formaldehyde gas sensor based on NiO nanowires. Vacuum. 2017;143:50-53.
    [Google Scholar]
  28. , . CRC Handbook of Chemistry and Physics (85th ed.). New York: CRC Press; .
  29. , , , . A comparative study of the thermal reactivities of some transition metal oxalates in selected atmospheres. Thermochim. Acta. 2005;429:57-72.
    [Google Scholar]
  30. , , , , , , , . Simple fabrication of porous NiO nanoflowers: growth mechanism, shape evolution and their application into Li-ion batteries. Int. J. Hydrogen Energy. 2017;42:7202-7211.
    [Google Scholar]
  31. , , , , , , , . Spectral and thermal characteristics of copper (II) carboxylates with fatty acid chains and their benzothiazole adducts. J. Therm. Anal. Calorim.. 2010;100:769-777.
    [Google Scholar]
  32. , , , , . The catalytic behavior of zinc oxide prepared from various precursors and by different methods. Mater. Res. Bull.. 2005;40:2089-2099.
    [Google Scholar]
  33. , , , , , . Influence of acid base properties of the support on the catalytic performances of Pt-based catalysts in a gas phase hydrogenation of acetonitrile. Appl. Catal. A. 2017;544:1-9.
    [Google Scholar]
  34. , , , . Sugar complexes with metal2+ ions: thermodynamic parameters of associations of Ca2+, Mg2+ and Zn2+ with galactaric acid. Carbohydr. Res.. 2000;336:55-61.
    [Google Scholar]
  35. Shanaj, B.R., John, X.R., 2016. Effect of calcination time on structural, optical and antimicrobial properties of nickel oxide nanoparticles. J. Theor. Comput. Sci. doi: 10.4172/2376-130X.1000149.
  36. , , , , , , , . Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity. Pure Appl. Chem.. 1985;57:603-619.
    [Google Scholar]
  37. , , . Dehydration of 2-butanol by a sulfated zirconia/γ-alumina mixed metal oxide catalyst inside a gas chromatograph injection port. Appl. Catal. A. 2003;246:227-235.
    [Google Scholar]
  38. , , , , , , . NiO nanoflakes: effect of anions on the structural, optical, morphological and magnetic properties. J. Magn. Magn. Mater.. 2017;441:787-794.
    [Google Scholar]
  39. , . Carbohydrate complexes with alkaline earth metal ions. Interaction of D-glucono-1,5-lactone with the Mg(II), Ca(II), Sr(II) and Ba(II) cations in the crystalline solid and aqueous solution. J. Inorg. Biochem.. 1990;39:33-41.
    [Google Scholar]
  40. , , , , , . Characterization and performance of the bifunctional platinum-loaded calcium hydroxyapatite in the one-step synthesis of methyl isobutyl ketone. J. Mol. Catal. A. 2013;377:42-50.
    [Google Scholar]
  41. , , , , , , . An experimental study in a jet-stirred reactor and a comprehensive kinetic mechanism for the oxidation of methyl ethyl ketone. Proc. Comb. Inst.. 2017;36:459-467.
    [Google Scholar]
  42. , , , , , . Sugar interaction with metal ions. FT-IR study on the structure of crystalline galactaric acid and its K+, NH4+, Ca2+, Ba2+, and La3+ complexes. Carbohydr. Res.. 2000;324:45-52.
    [Google Scholar]
  43. , , , , , , . High-performance electrode materials of hierarchical mesoporous nickel oxide ultrathin nanosheets derived from self assembled scroll-like α-nickel hydroxide. J. Power Sources. 2015;273:914-922.
    [Google Scholar]
  44. , , , , , , , . Facile synthesis of unique NiO nanostructures for efficiently catalytic conversion of CH4 at low temperature. Appl. Surf. Sci.. 2016;362:20-27.
    [Google Scholar]
  45. , , , , , , , , . Lactic acid production from rice straw in alkaline hydrothermal conditions in presence of NiO nanoplates. Catal. Today. 2016;274:40-48.
    [Google Scholar]
  46. , , , , , , , , . A facile homogeneous precipitation synthesis of NiO nanosheets and their applications in water treatment. Appl. Surf. Sci.. 2015;337:111-117.
    [Google Scholar]
  47. , , , , , , . Hierarchical flower-like nickel(II) oxide microspheres with high adsorption capacity of Congo red in water. J. Colloid Interface Sci.. 2017;504:688-696.
    [Google Scholar]

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