B. Paul, et al.
CatalysisCommunications132(2019)105804
and Ag, respectively. The main advantage of the synthesis procedure is
the in-situ synthesis of Ag/WO3 where no external reducing agent is
used, and the PEG played a dual role of surfactant and reducing agent
for Ag(I) (Scheme S1 in ESI). The same method has been proved to be
effective for large scale synthesis of the catalyst (batch scale up to 20 g).
The powder XRD patterns were recorded for identification of phases
exhibited by the synthesized materials. Fig. 1 shows the powder XRD
patterns of the synthesized Ag/WO3 catalyst. The diffraction peaks
matched well with the orthorhombic phase of WO3 (JCPDS File no.
89–4480, Fig. S1 in ESI). In addition, four diffraction peaks of face-
centered cubic Ag at 2θ values of 38.92, 44.98, 64.57, and 78.25 cor-
responds to (111), (200), (220), and (311) planes were observed
(JCPDS File no. 87–0720, Fig. S2 in ESI). The average crystallite sizes of
the synthesized NPs were estimated by the Debye-Scherrer equation
and were found to be 6.4 nm, and 8.72 nm modified with PEG 400 and
PEG 4000 respectively.
The SEM images of the catalysts prepared by PEG 400 and PEG 4000
are shown in (Figs. S3(a)) and S4(a) in ESI, respectively. The images
clearly indicate the formation of nearly uniform rod-like morphology of
the WO3 nanorod dotted with metallic Ag particles. The TEM image of
the nanomaterial synthesized in the presence of PEG 400 (Fig. S3 (b and
c)) shows Ag NPs of approximately sizes 20 nm randomly attached over
WO3 nanorods with diameter 100–350 nm. The fringes was found to be
separated by 0.39 nm and 0.21 nm, possibly due to (002) the (200)
plane of WO3 and metallic Ag respectively. Single crystalline nature of
the material was indicated by the electron diffraction (ED) pattern. The
composite synthesized in the presence of PEG 4000 (Fig. S4 (b and c))
also showed the rod-like structure of WO3 but with the much smaller
diameter of 20–40 nm and Ag NPs of sizes nearly 10 nm deposited over
WO3 nanorods. The lattice fringes were found to be separated by
0.38 nm and 0.2 nm, possibly due to the (002) and (200) plane of WO3
and metallic Ag, respectively. ED pattern indicated single-crystalline
nature of the material. The corresponding particle size histogram of Ag
(Figs. S3(f) and S4(f)), for catalysts prepared with PEG 400 and PEG
4000, respectively, exhibits narrow size distribution of the catalysts
between 16 and 20 nm and 6–10, respectively. Thus surfactant PEG of
higher molecular weight i.e. PEG 4000 has a superior effect in con-
trolling the dimension and dispersity of Ag/WO3 nanostructures.
Further evidence of the formation of Ag NPs supported on WO3 nanorod
is provided in Fig. 2, which clearly shows that considerable numbers of
Ag NPs are attached to the WO3 nanorods. The EDAX patterns (Fig. S5
(a,b) in ESI) also indicated the existence of Ag, W, and O in the syn-
thesized materials. The amount of Ag loaded in the catalysts was ana-
lyzed using ICP-AES technique.
Fig. 1. Powder XRD patterns of Ag/WO3 nanostructures.
2. Experimental
2.1. Synthesis of Ag/WO3 nanostructured catalyst in presence of PEG 400
and PEG 4000
In a typical procedure, 1.25 g of H2WO4 (0.5 mmol) and 0.016 g of
AgNO3 (0.1 mmol) were dissolved separately in a distilled water and
mixed together. Subsequently, 1 mmol of surfactant PEG 400 or PEG
4000 was added to the mixed solution. The pH was adjusted to ~9 by
drop wise addition of NH4OH solution. After 4 h of continuous stirring,
the yellow suspension was collected, washed with water/ethanol and
dried. The as-obtained solid powder was then calcined at 500 °C for 4 h
in a muffle furnace.
2.2. General procedure for the dehydrogenation of benzyl alcohols using
nanostructured Ag/WO3
Is discussed in the supporting information of the manuscript.
3. Results and discussion
Ag supported on WO3 nanocatalyst was synthesized in an aqueous
medium using tungstic acid and silver nitrate as precursor sources for W
Fig. 2. TEM images confirming the attachment of Ag particles over WO3 rod modified with (a) PEG 400, (b) PEG 4000.
2