A new mesoporous titanium-silicate Ti-MMM-2: a highly active and hydrothermally stable catalyst for H2O2-based selective oxidations
Introduction
The selective oxidation of organic compounds with an environmentally friendly oxidant, aqueous H2O2, in the presence of heterogeneous, easily recyclable catalysts is a challenging goal of fine chemistry [1], [2], [3]. Critical targets for catalytic technology using H2O2 are larger-pore analogues of titanium-silicate TS-1 [4]. In the past decade, a considerable amount of research was dedicated to the preparation of various titanium-containing mesoporous molecular sieves [5], [6], [7], [8], [9], [10], [11], [12]. Nevertheless, the problem of catalyst deactivation in the presence of aqueous H2O2 still restricts practical applications of these materials [2], [4], [9], [10], [11].
Recently, we reported that the mesoporous mesophase material, Ti-MMM (highly ordered titanium-silicate of the MCM-41-type synthesised under weakly alkaline conditions), shows high activity in H2O2-based oxidation of bulky organic substrates [12], [13], [14]. Meanwhile, hydrolytic instability of this material leads to a structure collapse during the oxidation process, which in turn results in a decrease of the catalytic activity after recycling [12], [13], [14]. It has been reported that mesoporous silicates of the SBA-15 family synthesised under strong acidic conditions possess a hydrothermal stability [15], [16], [17]; however, introduction of a heteroelement into the silicate matrix under strong acidic conditions is problematic [8], [16], [17]. Recently, we reported the preparation of Ti-SBA-15 under weakly acidic conditions [18]. This material showed stable catalytic properties but the activity was rather low because of thick silicate walls and poor titanium dispersion. Here, we present physicochemical and catalytic properties of the new highly active and hydrothermally stable mesoporous titanium-silicate, denoted as Ti-MMM-2, synthesised under moderately acidic conditions.
Section snippets
Materials
2,3,6-Trimethylphenol (TMP), methyl phenyl sulfide (MPS), (−)-caryophyllene (CP) and cetyltrimethyl ammonium bromide (CTAB) were purchased from Fluka and used without additional purification. A solution of TiOSO4·xH2SO4·xH2O (Aldrich) was used as received. Hydrogen peroxide (30%) was determined iodometrically prior to use. All the other reactants were obtained commercially and used without further purification.
Catalyst synthesis and characterisation
TS-1 (Si/Ti=30, DRS-UV: λmax=204 nm) was prepared according to Ref. [19]. Ti-MMM
Results and discussion
The physicochemical characteristics of Ti-MMM-2 are summarised in Table 1. According to XRD (Fig. 1) and nitrogen adsorption, the material has an ordered hexagonal arrangement of uniform mesopores with a diameter of d=3.2 nm and silicate wall thickness h=1.0 nm. Ordered mesopores are observed on the TEM image of Ti-MMM-2 (insert in Fig. 1). However, it should be mentioned that in general the structure of Ti-MMM-2 is less ordered compared to Ti-MMM and Ti-SBA-15, which is indicated by a larger
Acknowledgements
We thank T. Larina and V.A. Rogov for DRS-UV and GC–MS measurements. The financial support of Russian Foundation for Basic Research (grants 01-03-32852 and 01-03-32391) and INTAS (grant 2283) is highly appreciated. N.N. Trukhan acknowledges the financial support of CRDF (REC 008 grant).
References (26)
J. Dakka. Catal. Today
(1994)Adv. Catal.
(1996)- et al.
Appl. Catal. A: Gen.
(2001) - et al.
Appl. Catal. A: Gen.
(2001) - et al.
Micropor. Mesopor. Mater.
(2001) - et al.
J. Catal.
(2001) - et al.
Catal. Today
(2002) - et al.
Micropor. Mesopor. Mater.
(2003) - et al.
Micropor. Mesopor. Mater.
(1999) - et al.
Micropor. Mesopor. Mater.
(2001)
Catal. Today
Nucl. Instrum. Meth. A
Top. Catal.
Cited by (88)
H<inf>2</inf>O<inf>2</inf>-based selective epoxidations: Nb-silicates versus Ti-silicates
2019, Catalysis TodayCitation Excerpt :The potential of mesoporous titanium-silicates for the production of substituted benzoquinones using H2O2 has been recently discussed [15,16]. Although several types of hydrothermally stable and leaching-tolerant mesoporous Ti-silicates have been developed [10,11,17–20], the stability of Ti active sites toward progressive agglomeration under turnover conditions still remains a major concern if aqueous H2O2 is employed. In recent years, niobium-containing silicates have attracted great attention of the selective oxidation community.
Direct method for evaluation of BET adsorbed monolayer capacity
2017, Microporous and Mesoporous MaterialsTitania-silica monolithic multichannel microreactors. Proof of concept and fabrication/structure/catalytic properties in the oxidation of 2,3,6-trimethylphenol
2016, Microporous and Mesoporous MaterialsCatalytic activity and stability of carbon supported v oxides and carbides synthesized via pyrolysis of MIL-47 (V)
2016, Applied Catalysis A: GeneralCitation Excerpt :It should be noted that there have been substantial synthetic efforts to minimize V leaching from various silicate-based catalysts via V-tethering [13], grafting [11], incorporation [5,11,16], and immobilization [11,15,17]. However, the loss of active V species during the reactions was unavoidable due possibly to insufficient chemical stability between silicate and V species under the reaction conditions employed (Table S1) [20,35–37]. Carbon is a promising support material because it can provide several advantages such as high surface area [38–40], high dispersion of active V species [25,41], high resistance to thermochemical oxidation [42–44], and compatibility with a wide range of active V phases [25,45].
One-step solvent-free synthesis of cyclic carbonates by oxidative carboxylation of styrenes over a recyclable Ti-containing catalyst
2016, Applied Catalysis B: Environmental
- 1
Died on 6 July 2001.