Carbon Dioxide as a Soft Oxidant: Dehydrogenation of Ethylbenzene Into Styrene

We have been exploring various new catalyst systems for the utilization of carbon dioxide as a soft oxidant in the catalytic dehydrogenation of ethylbenzene (EB) to styrene. The utilization of CO2 as a soft oxidant for the commercially important catalytic dehydrogenation of EB to styrene has received enormous attention recently due to its several attractive features. This review summarizes the results of our most recent findings on zirconia-based composite oxide catalyst systems exploited for this reaction. Under this systematic and comprehensive investigation various zirconia-based composite oxide catalysts namely, TiO2-ZrO2, MnO2-ZrO2, CeO2-ZrO2, K2O/TiO2-ZrO2, B2O3/TiO2-ZrO2 and CeO2-ZrO2/SBA-15 have been synthesized, characterized by various techniques and evaluated for the title reaction. Most of these composite oxide catalysts were found to exhibit very interesting physicochemical characteristics and exceptionally better catalytic properties for this reaction. As revealed by characterization results, a large number of acid–base sites with moderate strength are essential for a high conversion and product selectivity of this reaction with CO2 as the soft oxidant.

Nanocasted oxides for oxidative dehydrogenation of ethylbenzene utilizing CO 2 as soft oxidant

Utilization of carbon dioxide as soft oxidant in the dehydrogenation of ethylbenzene over supported vanadium–antimony oxide catalysts

Styrene, an important monomer for synthetic polymers, is commercially produced by the ethylbenzene catalytic dehydrogenation (EBDH) process, which is thermodynamically limited and energy consuming. Alternative methods using oxygen as an oxidant are free from these disadvantages but have their own sets of challenges related to safety (the operations with potentially explosive oxygen-hydrocarbons mixtures) and substantial loss of styrene selectivity due to hydrocarbons total oxidation by this strong oxidant. Dehydrogenation of ethylbenzene in the presence of soft oxidant, carbon dioxide (CO2-EBDH), allows to produce styrene selectively with an energy-saving and environmentally friendly process as well as to effectively utilize CO2, a greenhouse gas. Several catalysts, mainly based on supported (on active carbon, alumina, MgO, TiO2, silicates, ZSM-5, MCM-41) or mixed oxides of Fe, Cr, and V were found to be efficient in the CO2-EBDH. 2-14 Among the best catalytic systems for this reaction, alumina supported V-Sb oxide catalyst demonstrates a very high styrene selectivity (97-98%) at high and stable time-on-stream activity. Zirconium oxide has received considerable attention not only as a promising catalyst for a number of reactions including hydrocarbons oxidative dehydrogenation (see Refs. in), but also as an active and “tunable” support with practically important chemical, thermal, and mechanical features. ZrO2 has bifunctional properties of acid and base along with reducing and oxidizing ability. Its high thermal stability is important as the CO2-EBDH is performed at high temperature of about 550-600 C. Like γ-alumina, zirconia is an excellent support for the synthesis of highly dispersed oxides, including VOx-species. 16,17 Also, in contrast with weaker interacting supports, zirconia inhibits the sintering of supported oxides in the presence of water at high temperatures. In general, zirconia has low surface area which, nevertheless, can be substantially increased by use of some special preparation methods. However, zirconia is more expensive than the traditional oxide materials such as alumina, silica, etc., and this is one of the reasons why attempts were made to explore the inherent favorable properties of both alumina and zirconia supports in a mixed Al-Zr oxide. There are several examples when Al2O3ZrO2 supported catalysts exhibited better catalytic properties than the catalysts supported on pure Al2O3 and ZrO2. 21,22,26

Two-step hydrothermally synthesized Ce1-xZrxO2 for oxidative dehydrogenation of ethylbenzene with carbon dioxide

The direct CO2 oxidative dehydrogenation of ethyl benzene (ODH-EB) is a great potential for the production of valuable styrene monomer. In contrast, past/present styrene (ST) synthesis is mainly obtained from oxidative dehydrogenation of ethyl benzene (EB) and being transformed into pilot scale under CO2 atmosphere. It was due to few unresolved restrictions existed in the synthesis of styrene monomer using the steam assisted process and commercial ST production technology. These problems are being rectified by ODH-EB process using CO2 as a soft oxidant. Therefore, ODH of EB is well-known high temperature process to convert the EB (petroleum by product) into valuable ST monomer through the utilizing of CO2. Present study clearly explains the concise history of dehydrogenation process used to convert EB to ST monomer, which is essential feedstock in the wide range of industrial commodities production. In this discussion we majorly devoted to design, development and synthesis of different Co based catalysts by applying different support materials such as SiO2, MgO, MgAl2O4 and γ-Al2O3 respectively. Moreover, this study extensively deals with chemical behavior of oxidants, utilization of viable active promoters and its characteristics features in the oxidative dehydrogenation process. Different reaction mechanisms in the ODH of EB process to describe CO2 utilization as well as surface styrene monomer formation and evaluation of other by products were discussed widely in this review paper. The surface acidic and basic chemistry of various support materials, its preparation, utilization and its catalytic activity applications have been discussed. Acidic–basic textural properties of different solid oxide support materials have been extensively illustrated through incorporation of variety active metallic oxide and promoters. The catalyst activity evaluation in ODH of EB process as well as plausible reaction mechanism of styrene monomer formation has been explained.

CO2 as a soft oxidant for oxidative dehydrogenation reaction: An eco benign process for industry

Oxidative dehydrogenation of ethylbenzene to styrene has been studied over Co3O4 supported on mesoporous silica (COK-12) with CO2 as soft oxidant in a fixed bed reactor at atmospheric pressure in the temperature range of 723 to 923K. While COK-12 has been prepared by self-assembly method using long chain ionic surfactant i.e., P123 as template, cobalt oxide supported on COK-12 catalysts with variable Co content have been synthesised by simple wet impregnation technique. All the catalysts were characterized by N2 adsorption - desorption, XRD, FT-IR, TPR, UV-Vis and XPS techniques. XRD and pore size distribution studies indicate the intactness of mesoporous structure of SiO2 even after incorporation of Co3O4. Presence of Co3O4 crystallites were observed beyond 5 wt% Co loading. High ethylbenzene conversion and stable styrene yields have been observed over 3% Co3O4/COK-12 catalyst due to the presence of large number of active Co3O4 catalytic sites. Enhancement in the activity has been observed with CO2 as soft oxidant than with N2 as diluent. This is because of the fact that the liberated H2 reacts with CO2 in the form of reverse water gas shift reaction.

La2O3 promotional effect to Co3O4/γ-Al2O3 catalyst in the oxidative dehydrogenation of ethylbenzene with CO2 as soft oxidant

Being an essential monomer in polymer industries, styrene's commercial production has gained much attention. Around 90% of the world's styrene production is accomplished via ethylbenzene dehydrogenation using excess superheated steam as a heat carrier. The cost linked with the production of enormous heat energy for the commercial process underlines the importance of finding alternative and innovative approaches for styrene production. Therefore, this chapter discusses the possible alternative routes of styrene production from ethylbenzene. The chapter begins with chemistry, thermodynamics, and a brief history, i.e. how the commercial method is established, of ethylbenzene dehydrogenation. Afterward, the possible alternative routes to commercial styrene production are listed and discussed. A particular emphasis is given to the preparation of styrene from ethylbenzene dehydrogenation using CO 2 as a soft oxidant because this method consumes CO 2 (one of the greenhouse gases) and emerges as a green chemistry process. The detailed mechanism of ethylbenzene dehydrogenation into styrene using CO 2 is studied. Significantly, the catalysts and their key properties during the ethylbenzene dehydrogenation to styrene with CO 2 are elucidated. Membrane technology is also briefly described together with the chemical looping technology.

The production of styrene (ST) by the petrochemical industry has traditionally relied on the ethylbenzenedehydrogenation (EB) reaction, using iron‐based catalysts. Estimates suggest that in 2025, the production of EB and ST will surpass 36 and 41 million tons, respectively. In this manner, the major aspects that led to the present stage of EB and ST production were described, discussing historical aspects, alternatives to produce these solvents, its characteristics, types of oxidants, and properties of iron‐based catalysts. Noteworthy advancements in this field include the utilization of CO2 as a soft oxidant and the employment of innovative catalysts derived from green synthesis methods. On the other hand, as an alternative to the fossil source for EB production, the utilization of lignin from biomass emerges as a promising eco‐friendly approach. The potential for implementing the ODH reaction in alternative reactors gives rise to questions regarding the necessity for industry to adapt to current climate needs. Furthermore, certain aspects of the mechanism have been called into question, as some fundamental points remain to be fully consolidated. These include the extent of the participation of CO2 in the reactivation of the active sites and the origin of the deposited coke.

Promoting effect of carbon dioxide on the dehydrogenation of ethylbenzene over silica-supported vanadium catalysts

This work presents that carbon dioxide, which is a main contributor to the global warming effect, could be utilized as a selective oxidant in the oxidative dehydrogenation of ethylbenzene. The dehydrogenation of ethylbenzene over alumina-supported vanadium-antimony oxide catalyst has been studied under different atmospheres such as inert nitrogen, steam, oxygen or carbon dioxide as diluent or oxidant. Among them, the addition of carbon dioxide gave the highest styrene yield (up to 82%) and styrene selectivity (up to 97%) along with stable activity. Carbon dioxide could play a beneficial role of a selective oxidant in the improvement of the catalytic behavior through the oxidative pathway.

N2 as a co-soft oxidant along with CO2 in ethylbenzene dehydrogenation to styrene over γ-Al2O3 supported Co–Mo nitride catalysts

Dehydrogenation of ethylbenzene with CO2 over porous Co/Al2O3–ZrO2 catalyst