Peter N. R. Vennestrøm

Beyond Petrochemicals: The Renewable Chemicals Industry

The use of renewable resources has attracted significant attention in recent years for many different reasons. 2] Renewable resources include electricity made from kinetic energy stored in wind, potential energy stored in water, thermal energy stored as heat underground and as solar influx in the form of electromagnetic radiation, and energy stored in chemical bonds in the case of biomass. Although renewable resources have been used for various purposes for centuries, there is currently a significant focus on expanding and optimizing this use in the form of new technologies fit for the 21st century. The use of biomass as a resource has developed rapidly in recent years, and it will become an important contributor to our available resources in the future. Biomass sets itself aside from the other renewable resources, since the energy it contains is stored as chemical bonds. This characteristic allows biomass to be used for several purposes apart from electricity and heat generation, such as the production of liquid fuels and chemicals. Indeed, biomass is the only renewable source of useful carbon atoms. Although biomass is annually renewable, it is still a scarce and limited resource, especially when produced in a sustainable manner, and it is important to use it in the most efficient way. This Essay argues for the production of select chemicals, thereby effectively replacing petroleum, as an efficient use and illustrates some of the current efforts that are made in the chemical industry towards adoption of biomass as a feedstock. Availability of Biomass Resources

Next-Generation Catalysis for Renewables: Combining Enzymatic with Inorganic Heterogeneous Catalysis for Bulk Chemical Production

Nowadays, production of bulk and commodity chemicals from renewable feedstocks is widely debated and investigated as an alternative to the fossil platform. The conversion of biomass necessitates the development of a new generation of catalysts that enable new kinds of reactions from a different chemical platform under different conditions than those conventionally employed. Indeed, new process and catalyst concepts need to be established. Both enzymatic catalysis (biocatalysis) and heterogeneous inorganic catalysis are likely to play a major role and, potentially, be combined. One type of combination involves one‐pot cascade catalysis with active sites from bio‐ and inorganic catalysts. In this article the emphasis is placed specifically on oxidase systems involving the coproduction of hydrogen peroxide, which can be used to create new in situ collaborative oxidation reactions for bulk chemical production.

Location of Cu2+ in CHA zeolite investigated by X-ray diffraction using the Rietveld/maximum entropy method

Rietveld/MEM analysis applied to synchrotron powder X-ray diffraction data of dehydrated CHA zeolites with catalytically active Cu2+ reveals Cu2+ in both the six- and eight-membered rings in the CHA framework, providing the first complete structural model that accounts for all Cu2+. Density functional theory calculations are used to corroborate the experimental structure and to discuss the Cu2+ coordination in terms of the Al distribution in the framework.

Redox‐Driven Migration of Copper Ions in the Cu‐CHA Zeolite as Shown by the In Situ PXRD/XANES Technique

Using quasi-simultaneous in situ PXRD and XANES, the direct correlation between the oxidation state of Cu ions in the commercially relevant deNOx NH3 -SCR zeolite catalyst Cu-CHA and the Cu ion migration in the zeolitic pores was revealed during catalytic activation experiments. A comparison with recent reports further reveals the high sensitivity of the redox-active centers concerning heating rates, temperature, and gas environment during catalytic activation. Previously, Cu+ was confirmed present only in the 6R. Results verify a novel 8R monovalent Cu site, an eventually large Cu+ presence upon heating to high temperatures in oxidative conditions, and demonstrate the unique potential in combining in situ PXRD and XANES techniques, with which both oxidation state and structural location of the redox-active centers in the zeolite framework could be tracked.

Chemoenzymatic Combination of Glucose Oxidase with Titanium Silicalite‐1

The use and integration of heterogeneous chemical catalysis and biocatalysis, especially using enzymes, will become increasingly important in a future chemical industry based on renewable resources. A range of alternative renewable chemical platforms have already been proposed from biomass, and compared to the conventional fossil-based platform these are radically different. The main difference lies in the high degree of oxyfunctionality of sugar molecules and (poly)alcohols compared to the low functionality of hydrocarbons and aromatics derived from crude oil. Consequently, the approaches for converting these alternative platforms are not identical. In conventional oil-based chemistry, functionality is introduced, whereas functionality should either be removed or used selectively when working with a renewable platform. Furthermore, biomass is usually in the solid form and the inherent oxyfunctionality renders it difficult, if not impossible, to use existing processes to convert the renewable platform into useful chemicals, because it is not easily handled in the gas phase. Therefore, the conversion of biomass will necessarily be carried out in the liquid (aqueous) phase. For the aforementioned reasons, there is now a need to develop a new generation of catalysts, which are able to facilitate the conversion of especially biomass-derived resources in the next generation of chemical processes. It will therefore be advantageous to combine the high stereo-, regio-, and chemoselectivity of enzymes with the diversity, tolerance, and ability of chemical catalysts to operate under various conditions and transform various substrates. In this way the advantages of each catalyst system may be exploited. 5] Additionally these advantages can be integrated and in some cases combined in heterogeneous one-pot reactions with enzymes or even using enzymes linked to the chemical catalyst to further intensify the process and to facilitate catalyst recycling and separation. One such system is the combination of oxidase enzymes with hydrogen peroxide-active titanium silicalite-1 (TS-1—a redox-active molecular sieve with MFI framework). Oxidases (E.C. 1.1.3) provide a useful catalytic approach to selective oxidation under mild conditions using air as a safe oxidant. They are probably more useful than oxygenases, given the need for expensive cofactors, which need to be recycled, when using the latter. This suggested combination has several advantages:

Fe-containing zeolites for NH3-SCR of NOx: effect of structure, synthesis procedure and chemical composition on catalytic performance and stability

The direct preparation of different iron-containing Beta and CHA zeolites has been attempted under diverse synthesis conditions, including in alkaline and fluoride media, to evaluate the influence of their physicochemical properties on the selective catalytic reduction (SCR) of NOx using NH3 as reductant. Of the different Fe-Beta zeolites, the sample prepared in the absence of alkali cations with a Si/Al ratio of around 13 showed high NO conversion values (>90 %). However, this catalyst suffered from severe deactivation when aged at high temperatures in the presence of steam. The preparation of more hydrophobic Fe-Beta zeolites did not improve the resistance of the catalyst against steam. In contrast, Fe-CHA zeolites prepared by a one-pot method under alkaline conditions with a Si/Al ratio of around 13 by using N,N,N-trimethyladamantylammonium as template not only showed excellent catalytic activity but also high hydrothermal stability, especially when sodium cations were selectively removed. Moreover, the Fe-CHA material synthesized by using the less expensive tetraethylammonium template also resulted in an active and hydrothermally stable catalyst.

Nitrate–nitrite equilibrium in the reaction of NO with a Cu-CHA catalyst for NH3-SCR

The equilibrium reaction between NO and Cu-nitrate, Cu(II)-NO3− + NO(g) ⇌ Cu(II)-NO2− + NO2(g), has been proposed to be a key step in the selective catalytic reduction of NO by ammonia (NH3-SCR) over Cu-CHA catalysts and points to the presence of Cu-nitrites. Whereas the formation of gaseous NO2 has been observed, a direct observation of Cu-nitrite groups under conditions relevant to NH3-SCR has been so far unsuccessful. In an effort to identify and characterize Cu-nitrites, the reaction between Cu-nitrates hosted in the CHA zeolite and NO is investigated by Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis) and X-ray absorption spectroscopy (XAS). We find that NO reacts with Cu-nitrates and that about half of the Cu-nitrate species are converted. After the reaction, the Cu(II) state is different from the original oxidized state. Analysis of XAS data indicates that the final state of the Cu-CHA catalyst is consistent with the partial conversion of the Cu-nitrate species to a bidentate Cu-nitrite configuration.

Iron-Containing SSZ-39 (AEI) Zeolite: An Active and Stable High-Temperature NH3-SCR Catalyst

The preparation of the iron‐containing SSZ‐39 zeolite is described for the first time through two different synthesis methods: post‐synthetic cation exchange and one‐pot synthesis. The nature and stability of the iron species within the different Fe‐SSZ‐39 materials have been studied through different characterization techniques, and their catalytic activity has been evaluated for the selective catalytic reduction (SCR) of NOx with ammonia. The directly synthetized Fe‐SSZ‐39 performs better for the SCR of NOx with ammonia than other related Fe‐zeolites, particularly at elevated reaction temperatures (above 450 °C), and presents improved hydrothermal stability when aged under severe conditions.

Tight bifunctional hierarchical catalyst

A new concept to prepare tight bifunctional catalysts has been developed, by anchoring CoMo(6) clusters on hierarchical ZSM-5 zeolites for simultaneous use in HDS and hydrocracking catalysis. The prepared material displays a significant improved activity in HDS catalysis compared to the impregnated counterpart.

Site-Specific Reactivity of Copper Chabazite Zeolites with Nitric Oxide, Ammonia, and Oxygen

In situ electron paramagnetic resonance (EPR) spectroscopy was applied to dilute copper chabazite (CHA) zeolites under gas flows relevant for the selective catalytic reduction of NO with ammonia (NH3‐SCR). Under both reducing and oxidizing conditions, we observed differences in reactivity between the different monomeric copper sites present: Upon reduction of Cu2+ with NO+NH3, the rate is seen to depend on the NH3 coverage. Subsequent oxidation with O2 resulted in a clean EPR spectrum of only one type of copper site, whereas oxidation with NO+O2 gave two types of copper sites. The rate of oxidation differed significantly between the reaction with O2 alone and with NO+O2 together. Thus, it was revealed that [Cu(NH3)2]+ complexes, which are regarded to be only weakly associated with the framework, nevertheless have different reactivity depending on the Al distribution in the proximity. The observed differences in reactivity of the copper sites have implications for the mechanistic understanding of NH3‐SCR with Cu zeolites.