Screening of different zeolite-based catalysts for gas-phase selective photooxidation of propan-2-ol

doi:10.1016/j.cattod.2007.09.005

Catalysis Today

Volume 129, Issues 1–2, 15 November 2007, Pages 102-109

https://doi.org/10.1016/j.cattod.2007.09.005 Get rights and content

Abstract

In the present piece of research photocatalytic activity of TiO₂ and V₂O₅ (as measured for gas-phase selective photoxidation of propan-2-ol) is substantially improved through their sol–gel synthesis on USY zeolites. The decrease in the crystallite size of TiO₂ (anatase) and V₂O₅ thus exhibiting the so-called quantum size effect (as determined by XRD and UV–vis spectroscopies, respectively) is to account for that. In the case of vanadium, the use of zeolites means a decrease in selectivity to acetone whereas no noticeable change is observed for titanium. Subsequent photodeposition of platinum on the Ti- and V-containing zeolites results in a sharp increase in molar conversion, low or negligible deactivation with a time-on-stream of 5 h and significant increase in selectivity to acetone which was in the range 90–96%.

Introduction

The main application of heterogeneous photocatalysis (at least as far as the number of the publications on the topic is concerned) is degradation of pollutants present in waters through complete mineralization [1], [2], [3]. One could think of the possibility of selectively oxidizing the pollutant to a non-toxic high-valued chemical which would be even more interesting though, unfortunately, it is not possible in aqueous media. There are some examples in the literature of selective adsorption of a chemical making use of the shape-selectivity (zeolites) [4] or the so-called adsorb-and-shuttle concept [5], [6]. These approaches allow selective adsorption though once adsorbed, the chemical will tend to be mineralized. Nevertheless, selective oxidations can be performed in non-aqueous media. Therefore, gas-phase selective oxidation of propan-2-ol to acetone is often used as a model reaction for characterization of photocatalytic activity [7], [8], [9].

As regards the photocatalyst itself, titania is by far the most-widely used system, but it has some drawbacks such as the absorption in the UV-region or the low surface area. In this sense, as pointed out by Corma and García [10], some of the advantages of using zeolites in photocatalysis are as follows:

(i)
High surface area, thus enabling high adsorption of chemicals to be photo-oxidised/reduced.
(ii)
Transparency to UV–vis radiation above 240 nm thus allowing a certain penetration of the exciting light into the powder which can be useful in order to allow exciting light to reach a photoactive guest.
(iii)
Possibility to vary the chemical composition of framework and out-of-framework position in a large extent, thus rendering these molecular sieves photoactive (e.g. introducing Ti or V atoms).
(iv)
Possibility to modulate both the micropolarity of the zeolite interior and the size of the channels.

Two of the most common methods of preparation of titania into zeolites are ion exchange from titanyl solutions [11], [12] or hydrolysis of titanium alkoxide [13], [14].

The relatively high electron–hole recombination rate of TiO₂ constitutes an additional drawback since it is detrimental to its activity. In this sense, doping with metals could make a double effect: (i) firstly, it could reduce the band gap energy, thus shifting the absorption band to the visible region and (ii) secondly, metals could provoke a decrease in electron–hole recombination rate, acting as electron traps.

The present piece of research is aimed at exploring the possibility of improving the photocatalytic activity of titania, vanadia and zinc oxide through their sol–gel synthesis on USY zeolites and the subsequent doping with Pt or Ag.

Section snippets

Synthesis of Ti, V and Zn-containing zeolites

Zeolite-based photocatalysts were synthesized through the sol–gel method starting from titanium isopropoxide [Ti(OCH(CH₃)₂)₄,] vanadyl acetylacetonate [VO(acac)₂] and zinc acetylacetonate [Zn(acac)₂] which were incorporated, in a nominal content of 2 mmol/g of catalyst, on USY (Si/Al = 62 and 4.7) zeolites.

In order to obtain titanium-containing systems, 10 g of zeolite previously treated at 400 °C in air flow for 4 h were introduced in a 250 mL round-bottom flask together with 60 mL of propan-2-ol and

First screening and characterization of the most active systems

Results found for the systems of vanadium and titanium incorporated to USY zeolites in the gas-phase selective oxidation of propan-2-ol are given in Fig. 1. For the sake of comparison, those achieved with the corresponding pure vanadia and titania systems have also been included. Zn-containing systems are not represented since they gave molar conversions below 1%. Therefore, such systems were already ruled out at the early stages of the screening.

For all the systems studied in the present work,

Conclusions

The above-mentioned results allow us to draw the following conclusions:

The sol–gel synthesis of titania and vanadia on USY zeolites led to an improvement in photocatalytic activity for gas-phase photoselective oxidation of propan-2-ol. XRD, Raman and FT-IR spectroscopies allowed us to conclude that the systems were constituted by titania (anatase) or vanadia particles with a lower crystal size than the corresponding pure TiO₂ and V₂O₅ systems. The decrease of crystal size is probably to account

Acknowledgments

The authors gratefully acknowledge the financial support from Ministerio de Educación y Ciencia (Project CTQ-2005-04080/BQU) and Junta de Andalucía (Project FQM 191) both co-funded with FEDER.

References (33)

J.M. Herrmann
Catal. Today
(1999)
P. Fernández et al.
Catal. Today
(2005)
Y. Paz
C.R. Chimie
(2006)
Y. Sagatelian et al.
J. Photochem. Photobiol. A
(2005)
A. Sclafani et al.
J. Catal.
(1997)
U.R. Pillai et al.
J. Catal.
(2002)
S. Anandan et al.
J. Photochem. Photobiol. C
(2003)
K. Hashimoto et al.
Appl. Catal. B
(2001)
H. Yahiro et al.
Catal. Today
(2007)
M.A. Aramendía et al.
Catal. Today
(2005)

J.C. Colmenares et al.

Appl. Catal. A

(2006)

W.X. Zhang et al.

Catal. Today

(1998)

M. Kang et al.

Appl. Catal. B

(2004)

S.V. Awate et al.

J. Mol. Catal. A

(2005)

M. Anpo et al.

J. Catal.

(2003)

N. Jagtap et al.

Appl. Clay Sci.

(2006)

Cited by (21)

Zein films with ZnO and ZnO:Mg quantum dots as functional nanofillers: New nanocomposites for food package with UV-blocker and antimicrobial properties
2020, Polymer Testing
The preparation of a new nanocomposite by combining zein and quantum dots (QDs) was the main interest of the present work. By the sol-gel method, colloidal ethanolic dispersions of zinc oxide (ZnO) particles and ZnO particles doped with magnesium (II) (ZnO:Mg) were obtained, sized 4.26 and 3.65 nm, respectively, as determined by UV–Vis spectroscopy. The prepared QDs were used as nanofillers in order to obtain zein-based nanocomposite films, which displayed good visual appearance, homogeneity, and transparency. The presence of QDs increased the hydrophobicity and reduced, up to three times, the amount of water uptake of the composite films when compared to pure zein. Those effects were more pronounced for ZnO:Mg QDs. TEM, FTIR, and fluorescence microscopy analysis indicated that zein interacts more effectively with ZnO:Mg than with ZnO. In addition, and most importantly, the presence of QDs in the films showed an important advantage when compared to those of pure zein: the extended UV-blocking in the absorbance spectra. The antimicrobial assays demonstrated that the ZnO NPs, loaded into zein films, are promising antibacterial materials since the inhibition of growth of S. aureus reached (96.5 ± 4.9)% at 44.8 wt% of ZnO NPs. Therefore, the nanocomposites show promising features for the development of food packaging, UV protective films, and for the development of new and sustainable materials.
Photocatalytic and photothermocatalytic applications of cerium oxide-based materials
2019, Cerium Oxide (CeO2): Synthesis, Properties and Applications
Cerium dioxide (CeO₂) presents unique properties as the special electronic and optical properties of the 4f electrons, the capacity to form nonstoichiometric oxygen-deficient CeO_2 − x oxides, the high oxygen mobility, and the reversible transformation between Ce^4 + and Ce^3 + that make it interesting for photocatalytic applications. CeO₂ is a wide bandgap semiconductor (3.0–3.4 eV), but different approaches as combination with oxides, deposition of noble metals, doping with metal and nonmetal species, and the formation of surface defects have been adopted to extend its absorption towards the visible region with the aim to improve its photocatalytic performance. Cerium oxide-based materials have been used as photocatalysts for degradation of harmful compounds in water and air effluents with some attention also to photothermal catalytic reactions, for selective oxidation reactions, CO₂ reduction, and water splitting. Some examples of all of these topics are described in the following chapter.
Enhanced photocatalytic activity of supported TiO<inf>2</inf> by selective surface modification of zeolite y
2016, Applied Surface Science
Citation Excerpt :
Upon loading 20% of TiO2 to both parent and treated zeolites, the absorbance edge of the materials is extended. The absorbance edge of the loaded zeolites showed blue shift as compared with the absorbance of pure TiO2 [34,35]. In Fig. 4, the absorption band at around 200–240 nm is due to electron transfer excitation from the ligand-oxygen to an unoccupied orbital of the Ti4+ framework.
Zeolite Y was treated using ammonium acetate and ammonium fluoride sequentially. As a consequence the aluminum from the surface was selectively removed. Then, loading with TiO₂ (20 wt%) led to a final photocatalyst. The samples were characterized by X-ray diffraction (XRD), elemental analysis (ICP-OES), N₂ adsorption, diffuse reflectance UV–vis spectroscopy (DRS), photoluminescence spectroscopy (PL), and X-ray photoelectron spectroscopy (XPS). It was found that 50% of the Al atoms were removed from the surface of the zeolite without affecting the framework structure. The TiO₂/treated zeolite sample yielded 92% photocatalytic degradation of 10 ppm methyl orange (MO), a model pollutant, while the TiO₂/parent zeolite converted only 7.6%. The mass normalized turnover rate (TOR_m) of the treated zeolite loaded with TiO₂ was about 12 times higher than that of the parent zeolite loaded with the same amount of TiO₂ precursor. This higher photocatalytic activity of the TiO₂ supported on treated zeolite can be attributed to a more efficient interaction of the TiO₂ with the zeolite leading to higher adsorption capacity. Reusability of the photocatalysts was assessed by performing three consecutive reaction cycles that showed no significant loss of photocatalytic activity.
Selective photooxidation of alcohols as test reaction for photocatalytic activity
2012, Applied Catalysis B: Environmental
Citation Excerpt :
All the titanium-based systems were also tested for gas-phase selective photooxidation of 2-propanol. In this case, optimization of reaction conditions and mechanistic discussions were already described in previous studies [25–27]. Therefore, we will focus now on the catalytic results for the 25 different titania-based systems used in the present study.
Twenty-four different titania-based systems synthesized through the sol–gel process varying the precursor (titanium isopropoxide or tetrachloride) and/or the ageing conditions (magnetic stirring, ultrasounds, microwave or reflux) were tested for liquid-phase selective photooxidation of 2-butenol (crotyl alcohol) to 2-butenal (crotonaldehyde) and gas-phase selective photooxidation of 2-propanol to acetone. To the best of our knowledge, the former process is suggested for the first time as test reaction for photocatalytic activity. Interestingly, both test reactions (despite having very different reactant/catalyst ratio and contact times) showed quite similar results in terms of influence of the precursor (titanium isopropoxide leading to better results than titanium tetrachloride) and the metals (the presence of iron, palladium or zinc being detrimental to activity whereas zirconium and especially gold improved the results as compared to pure titania). To our mind, these results give validity to both processes as test reactions for a fast screening of catalysts for photocatalytic tranformations. Finally, some gold-containing solids even improved photocatalytic activity of Degussa P25.
Synthesis and characteristics of natural zeolite supported Fe <sup>3+</sup> -TiO <inf>2</inf> photocatalysts
2011, Applied Surface Science
Citation Excerpt :
Of various substrates, zeolites have been most favorable to be used in supporting TiO2, due to their unique structures, uniform pores and channels and excellent absorption ability [4]. Previous works have mainly emphasized on the synthetic zeolites such as ZSM-5 [5], A-zeolite [5], HZSM-5 [6,9,10], MCM41 [7], X-zeolites [7], Y-zeolite [7,8], HY-zeolites [9,10], Hb-zeolites [9], Hβ-zeolite [10], β-zeolite [11], USY-zeolite [12], MOR-zeolite [13], etc., as the substrates of TiO2. TiO2 supported on zeolite integrates the photocatalytic activity of TiO2 with the adsorption properties of zeolite together, which induce a synergistic effect, resulting in the enhancement of photocatalytic efficiency [4].
Natural zeolite supported Fe³⁺-TiO₂ photocatalysts were synthesized for the sake of improving the recovery and photocatalytic efficiency of TiO₂. The as-prepared materials were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflection spectroscopy (UV–vis DRS), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). Methyl orange was used to estimate the photocatalytic activity of the samples. The results showed that zeolite inhibited the growth of TiO₂ crystallite sizes. The Fe³⁺ concentration played an important role on the microstructure and photocatalytic activity of the samples. The iron ions could diffuse into TiO₂ lattice to the form Fe–O–Ti bond and gave TiO₂ the capacity to absorb light at lower energy levels. The photocatalytic activity of the samples could be enhanced as appropriate dosages of Fe³⁺ were doped.
Catalytic photodegradation of dyes by in situ zeolite-supported titania
2010, Chemical Engineering Journal
The degradation of dyes (methylene blue, direct blue 71, direct yellow 8) by a series of titania-supported catalysts generated in situ via the impregnation of TiCl₄ onto a series of zeolite, which was synthesized using rice husks as the silicon source, was individually evaluated. After calcination, the resulting supported catalysts were characterized by X-ray diffraction spectrometry, ultraviolet–visible diffuse reflectance spectroscopy, diffuse reflectance and transmittance infrared Fourier transform spectroscopy, energy dispersive X-ray scanning electron microscopy, small angle X-ray scattering and differential pulse voltammetry. The titania generated is present in the anatase phase, without affecting the zeolite framework. Catalyst activity was shown to be comparable to that of the commercial P-25 catalyst after 1 h of UV light exposition. Monitoring the catalyst performance of several batches of material showed that P-25 provided the highest photodecomposition until the third cycle. On the other hand, the activity of the in situ-supported titania catalyst, in spite of showing lower catalytic activity, remained roughly constant up to the fifth cycle. This suggests that the catalyst generated in situ is more suitable for both filtering and reuse.

View all citing articles on Scopus

View full text

Screening of different zeolite-based catalysts for gas-phase selective photooxidation of propan-2-ol

Abstract

Introduction

Section snippets

Synthesis of Ti, V and Zn-containing zeolites

First screening and characterization of the most active systems

Conclusions

Acknowledgments

Catal. Today

Catal. Today

C.R. Chimie

J. Photochem. Photobiol. A

J. Catal.

J. Catal.

J. Photochem. Photobiol. C

Appl. Catal. B

Catal. Today

Catal. Today

Appl. Catal. A

Catal. Today

Appl. Catal. B

J. Mol. Catal. A

J. Catal.

Appl. Clay Sci.