Mesoporous sol-gel silica supported vanadium oxide as effective catalysts in oxidative dehydrogenation of propane to propylene

Vanadium oxide incorporated mesoporous silica (V-m-SiO₂) were designed and synthesized using a surfactant-modified sol-gel method. Detailed characterization shows that monomeric [VO₄] sites containing one terminal V[double bond, length as m-dash]O bond and three V-O-support bonds are dominated until atomic ratio of vanadium to silicon approaches to 5%. It is also confirmed that such V-m-SiO₂ catalyst contains high proportion of vanadium oxide species interacting strongly with silica. Compared to vanadium oxide supported mesoporous silica (V/m-SiO₂) prepared using a traditional impregnation method, present V-m-SiO₂ catalyst exhibits more superior ability to catalyze oxidative dehydrogenation of propane to propylene. By correlation with structural data, superior catalytic performance of present V-m-SiO₂ catalyst can be reasonably attributed, in part, to its favorable geometric and electronic properties rendered by the unique preparation method.

Recent Advances in the Applications of Mesoporous Silica in Heterogenous Catalysis

Mesoporous silica is a class of silica material with a large specific surface area, high specific pore volume and meso-sized pores. These properties make mesoporous silica a good choice of...

Role of CO2 During Oxidative Dehydrogenation of Propane Over Bulk and Activated-Carbon Supported Cerium and Vanadium Based Catalysts

CeO2, V2O5 and CeVO4 were synthesised as bulk oxides, or deposited over activated carbon, characterized by XRD, HRTEM, CO2-TPO, C3H8-TPR, DRIFTS and Raman techniques and tested in propane oxidative dehydrogenation using CO2. Complete oxidation of propane to CO and CO2 is favoured by lattice oxygen of CeO2. The temperature programmed experiments show the ~ 4 nm AC supported CeO2 crystallites become more susceptible to reduction by propane, but less prone to re-oxidation with CO2 compared to bulk CeO2. Catalytic activity of CeVO4/AC catalysts requires a 1–2 nm amorphous CeVO4 layer. During reaction, the amorphous CeVO4 layer crystallises and several atomic layers of carbon cover the CeVO4 surface, resulting in deactivation. During reaction, V2O5 is irreversibly reduced to V2O3. The lattice oxygen in bulk V2O5 favours catalytic activity and propene selectivity. Bulk V2O3 promotes only propane cracking with no propene selectivity. In VOx/AC materials, vanadium carbide is the catalytically active phase. Propane dehydrogenation over VC proceeds via chemisorbed oxygen species originating from the dissociated CO2.

Graphic Abstract

Oxidative dehydrogenation of light alkanes to olefins on metal-free catalysts

Metal-free boron- and carbon-based catalysts have shown both great fundamental and practical value in oxidative dehydrogenation (ODH) of light alkanes. In particular, boron-based catalysts show a superior selectivity toward olefins, excellent stability and atom-economy to valuable carbon-based products by minimizing CO2 emission, which are highly promising in future industrialization. The carbonaceous catalysts also exhibited impressive behavior in the ODH of light alkanes helped along by surface oxygen-containing functional groups. This review surveyed and compared the preparation methods of the boron- and carbon-based catalysts and their characterization, their performance in the ODH of light alkanes, and the mechanistic issues of the ODH including the identification of the possible active sites and the exploration of the underlying mechanisms. We discussed different boron-based materials and established versatile methodologies for the investigation of active sites and reaction mechanisms. We also elaborated on the similarities and differences in catalytic and kinetic behaviors, and reaction mechanisms between boron- and carbon-based metal-free materials. A perspective of the potential issues of metal-free ODH catalytic systems in terms of their rational design and their synergy with reactor engineering was sketched.

Propane Oxidative Dehydrogenation on Vanadium-Based Catalysts under Oxygen-Free Atmospheres

Catalytic propane oxidative dehydrogenation (PODH) in the absence of gas phase oxygen is a promising approach for propylene manufacturing. PODH can overcome the issues of over-oxidation, which lower propylene selectivity. PODH has a reduced environmental footprint when compared with conventional oxidative dehydrogenation, which uses molecular oxygen and/or carbon dioxide. This review discusses both the stoichiometry and the thermodynamics of PODH under both oxygen-rich and oxygen-free atmospheres. This article provides a critical review of the promising PODH approach, while also considering vanadium-based catalysts, with lattice oxygen being the only oxygen source. Furthermore, this critical review focuses on the advances that were made in the 2010–2018 period, while considering vanadium-based catalysts, their reaction mechanisms and performances and their postulated kinetics. The resulting kinetic parameters at selected PODH conditions are also addressed.

Oxidative dehydrogenation of propane on silica-supported vanadyl sites promoted with sodium metavanadate

[VO₄]/SiO₂ promoted with NaVO₃ polymorphs (α or β) shows higher initial activity in oxidative dehydrogenation of propane (increase by 30 and 125%, respectively) compared to that of unpromoted [VO₄]/SiO₂ at similar vanadium loadings.

Oxidative dehydrogenation of propane over transition metal sulfides using sulfur as an alternative oxidant

Sulfur vapor (S₂) is explored as a “soft” oxidant for the selective catalytic dehydrogenation of propane to propylene over a variety of metal sulfide surfaces.

Serendipity in Catalysis Research: Boron-Based Materials for Alkane Oxidative Dehydrogenation

Light olefins such as ethylene and propylene form the foundation of the modern chemical industry, with yearly production volumes well into the hundreds of millions of metric tons. Currently, these light olefins are mainly produced via energy-intensive steam cracking. Alternatively, oxidative dehydrogenation (ODH) of light alkanes to produce olefins allows for lower operation temperatures and extended catalyst lifetimes, potentially leading to valuable process efficiencies. The potential benefits of this route have led to significant research interest due to the wide availability of natural gas from shale deposits. Advances in this area have still not yielded catalysts that are sufficiently selective to olefins for industrial implementation, and ODH still remains a holy grail of selective alkane oxidation research. The main challenge in selective oxidation lies in preventing the overoxidation of the desired product, such as propylene during propane oxidation, to CO and CO₂. Research into selective heterogeneous catalysts for the oxidative dehydrogenation of propane has led to the extensive use of vanadium oxide-based catalysts, and studies on the surface mechanism involved have been used to improve the catalytic activity of the material. Despite decades of research, however, selectivity toward propylene has not proven satisfactory at industrially relevant conversions. It is imperative for new catalytic systems that minimize product overoxidation to be developed for future applications of oxidative dehydrogenation processes. While rational catalyst design has been successful in developing homogeneous catalyst systems, its practical use in heterogeneous catalyst development remains modest. The complexity of surfaces with a variety of terminations and bulk structures, let alone their modification by the chemical potential of a reaction mixture, makes heterogeneous catalyst discovery serendipitous in many cases. The catalyst family presented in this Account is no exception. The importance of catalysis research lies in exploring the science behind serendipity. In this Account, we will first present our initial discovery of boron nitride (BN) as an unexpected catalyst for the oxidative dehydrogenation of light alkanes. Beyond its surprising activity, BN also drew interest due to its low selectivity to carbon oxides. This observation made BN distinct from previously studied metal oxide catalysts for selective alkane oxidation. We narrowed down its unique reactivity to the oxygen functionalization of the catalyst surface, particularly the formation of B-O species as probed by various spectroscopic techniques. In investigating the critical role of each of the structural elements during ODH, we discovered that not only BN but an entire class of boron-containing compounds are active and selective for the formation of propylene from propane. All these materials form a complex oxidized surface with a distribution of BO _x surface sites. This discovery opens the doors to a new field of boron-based oxidation chemistry that currently has more questions than answers. We aim to make this Account a starting point for the research community to explore these new materials to understand their surface mechanisms and the surface species that offer a unique selectivity toward olefinic products. Effective use of these materials may lead to novel processes for efficient use of abundant light alkane resources by oxidation chemistry.

Shale Gas Implications for C2-C3 Olefin Production: Incumbent and Future Technology

Substantial natural gas liquids recovery from tight shale formations has produced a significant boon for the US chemical industry. As fracking technology improves, shale liquids may represent the same for other geographies. As with any major industry disruption, the advent of shale resources permits both the chemical industry and the community an excellent opportunity to have open, foundational discussions on how both public and private institutions should research, develop, and utilize these resources most sustainably. This review summarizes current chemical industry processes that use ethane and propane from shale gas liquids to produce the two primary chemical olefins of the industry: ethylene and propylene. It also discusses simplified techno-economics related to olefins production from an industry perspective, attempting to provide a mutually beneficial context in which to discuss the next generation of sustainable olefin process development.

Oxidative Dehydrogenation of Propane over a High Surface Area Boron Nitride Catalyst: Exceptional Selectivity for Olefins at High Conversion

Developing environment-friendly active and selective catalysts for oxidative dehydrogenation of propane for on-purpose propene synthesis is challenging despite tremendous industrial potential for this reaction. Herein, we report on catalytic activity of high surface area hexagonal boron nitride, toward oxidative dehydrogenation of propane. It shows remarkable selectivity for alkenes (∼70%) at very high conversion (of ∼50%) of propane. Propene and ethene selectivities as high as 53 and 18%, respectively, were obtained at a conversion of 52%. The catalytic activity is retained continuously for 5 h. Regeneration in ammonia brings back the catalytic activity to its full potential. Oxidation of surface B-N bonds in oxygen leads to the diminishing catalytic activity after 5 h which, on heating in ammonia, reduced back to their native form, regaining the indigenous activity. Remarkably, the addition of ammonia in the reaction feed showed stable activity for more than 100 h.

Progress in selective oxidative dehydrogenation of light alkanes to olefins promoted by boron nitride catalysts

We highlight recent progress on a newly-developed catalyst system, boron nitride, for selective oxidative dehydrogenation of light alkanes.

Selective oxidative dehydrogenation of propane to propene using boron nitride catalysts

The exothermic oxidative dehydrogenation of propane reaction to generate propene has the potential to be a game-changing technology in the chemical industry. However, even after decades of research, selectivity to propene remains too low to be commercially attractive because of overoxidation of propene to thermodynamically favored CO₂ Here, we report that hexagonal boron nitride and boron nitride nanotubes exhibit unique and hitherto unanticipated catalytic properties, resulting in great selectivity to olefins. As an example, at 14% propane conversion, we obtain selectivity of 79% propene and 12% ethene, another desired alkene. Based on catalytic experiments, spectroscopic insights, and ab initio modeling, we put forward a mechanistic hypothesis in which oxygen-terminated armchair boron nitride edges are proposed to be the catalytic active sites.

Morphological investigations of nanostructured V2O5 over graphene used for the ODHP reaction: from synthesis to physiochemical evaluations

Several V₂O₅ nanostructures, including the rod or belt-like, tube-like, needle-like and flower-like, were synthesized via the reflux and hydrothermal processes utilizing different templates such as monoamine, diamine, aromatic and alcoholic amines

Carbon nanofibers modified with heteroatoms as metal-free catalysts for the oxidative dehydrogenation of propane

Carbon nanofibres (CNFs) were modified with B and P by an ex situ approach. In addition, CNFs doped with N were prepared in situ using ethylenediamine as the N and C source. After calcination, the doped CNFs were used as catalysts for the oxidative dehydrogenation of propane. For B-CNFs, the effects of boron loading and calcination temperature on B speciation and catalytic conversion were studied. For the same reaction temperatures and conversions, B- and P-doped CNFs exhibited higher selectivities to propene than pristine CNFs. The N-CNFs were the most active but the least selective of the catalysts tested here. Our results also show that the type of P precursor affects the selectivity to propene and that CNFs modified using triphenylphosphine as the precursor provided the highest selectivity at isoconversion.