Elsevier

Catalysis Communications

Volume 27, 5 October 2012, Pages 154-158
Catalysis Communications

Short Communication
Dehydrogenation and Diels–Alder reactions in a one-pot synthesis of benzaldehyde from n-butane over acid catalysts

https://doi.org/10.1016/j.catcom.2012.07.014Get rights and content

Abstract

VOx/ZrO2/SiO2 catalysts were synthesized via grafting of vanadium and zirconium alkoxides over Aerosil 380. With these materials the formation of benzaldehyde from butane was possible in a one-pot synthesis, where oxidative dehydrogenation (ODH) for the formation of butadiene is coupled with a Diels–Alder reaction for the formation of benzaldehyde. Experiments performed with a catalyst where the support was modified with Ce instead of Zr, give a material that under the reaction conditions studied does not yield benzaldehyde, showing that acidity plays an important role in the formation of this compound.

Graphical abstract

Highlights

► Benzaldehyde was produced from n-butane in a one-pot synthesis at 400 °C. ► The reaction occurred over vanadium supported on Ce or Zr modified SiO2. ► The formation of benzaldehyde occurred only on catalysts with acid sites. ► Catalysts with strong acid sites showed high selectivity to CO and CO2. ► The reaction network consists of Diels–Alder and oxidative dehydrogenation steps.

Introduction

Benzaldehyde (BZ) is an aromatic aldehyde widely used in the food industry as a flavoring agent, and in the cosmetics and personal care products as a fragrance [1]. Even when it is extracted from natural sources, most of the benzaldehyde for industrial application stems from the chlorination and oxidation of toluene. These processes either require the use of organic solvents, which are not environmentally friendly, or may produce a chlorine contaminated benzaldehyde that is not acceptable in the pharmaceutical and food industries [2].

There is an ongoing search for alternative technologies with special emphasis in the partial oxidation of benzyl alcohol and styrene oxidation [3], [4], [5]. Nevertheless, there is not a process yet that can be industrially scaled to satisfy the requirements of the food and pharmaceutical industry.

In this work, we explore an alternative for the production of benzaldehyde based on the use of n-butane as starting material. Use of n-butane as a feedstock has been studied and used for several applications that involve partial oxidation and oxidative dehydrogenation reactions (ODH) [6], [7]. The catalytic production of olefins from alkanes using ODH is a very attractive process that offers the possibility of reducing the energy consumption in the reactor, where the energy demands of the ODH are satisfied by the heat released in the alkane oxidation. With the right type of catalyst the selectivity to olefins could be favored over CO y CO2 formation, making possible the conversion of n-butane to butadiene with high yield. Controlling the reaction conditions, it might be possible to produce also compounds that could act as a dienophile in a cycloaddition reaction, such as the Diels–Alder, with the butadiene as the conjugated diene, making possible the formation of compounds containing an unsaturated six-membered ring. If the catalyst shows selectivity to the formation of acrolein, the reaction product will be an aldehyde that via oxidative dehydrogenation produces benzaldehyde. A similar approach has been suggested by Izawa et al. [8] for the production of phenols using a catalyst for dehydrogenation, but starting with the Diels–Alder reaction. In this work we show that it is possible to start with the alkane and in one pot reaction to produce the aromatic molecule with the aid of a catalyst.

Acid properties as well as particle size of the catalyst play an important role on both catalytic activity and selectivity. In this regard, ZrO2 is an interesting material because of its acidic properties, and if V is supported on it, the production of olefins from butane is observed [9], [10]. However, bulk ZrO2 has a low surface, but a non-acidic material such as SiO2 can be used as a support to increase the surface area. For this work the catalysts were prepared with V supported on Zr grafted on SiO2; for comparison purposes, non-acidic materials were prepared with Ce instead of Zr.

Section snippets

Catalyst synthesis

Catalysts 10 VZrS and 20 VZrS: ZrO2–SiO2 mixed oxide supports were prepared by contacting an appropriate amount of Zirconium(IV) n-butoxide (Aldrich, 80%) with 473 K dried, pure silica (Degussa, Aerosil 380 m2/g) to give surface Zr densities of 4 and 8 atom Zr/nm2. During this procedure the solid powder was maintained 12 h continuously immersed and stirred under toluene reflux at room temperature. The solids were then dried and calcined in flowing oxygen at 673 K for 8 h, before contacting with

Catalyst and support characterization

Table 1 summarizes the composition of each catalyst and the BET surface areas calculated from the N2 physisorption data. After grafting/impregnation, all the surface areas experienced an area reduction (up to 55%) from the original Aerosil (380 m2/g). For the Zr materials, the X-ray diffraction pattern shows only the amorphous nature of pure silica in the 10 VZrS material, suggesting that with the grafting method, high dispersions of zirconium and vanadium species on the surface were achieved (

Conclusions

This work shows the feasibility of having a process for the production of benzaldehyde from a chlorine free feedstock, coupling a Diels–Alder reaction with the ODH of n-butane. This one-pot synthesis is possible over catalysts that favor the formation of dehydrogenation products of butane to produce butadiene, and partial oxidation products to form acrolein. The butadiene acts as a diene in a Diels–Alder reaction with the acrolein, the dienophile, to form 3-cyclohexene-1-carboxaldehyde that

Acknowledgments

The authors acknowledge the support received for the CONACYT fellowship 203704, and the financial support from the PIFI fund for academic groups SMCTSM AC B-26 P/CA32-2006-24-20, P/CA32-PIFI2007-24-29 and P/PIFI 2008-24MSUOO11E-06.

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