Next-generation feedstocks methanol and ethylene glycol and their potential in industrial biotechnology

Microbial fermentation processes are expected to play an important role in reducing dependence on fossil-based raw materials for the production of everyday chemicals. In order to meet the growing demand for biotechnological products in the future, alternative carbon sources that do not compete with human nutrition must be exploited. The chemical conversion of the industrially emitted greenhouse gas CO2 into microbially utilizable platform chemicals such as methanol represents a sustainable strategy for the utilization of an abundant carbon source and has attracted enormous scientific interest in recent years. A relatively new approach is the microbial synthesis of products from the C2-compound ethylene glycol, which can also be synthesized from CO2 and non-edible biomass and, in addition, can be recovered from plastic waste. Here we summarize the main chemical routes for the synthesis of methanol and ethylene glycol from sustainable resources and give an overview of recent metabolic engineering work for establishing natural and synthetic microbial assimilation pathways. The different metabolic routes for C1 and C2 alcohol-dependent bioconversions were compared in terms of their theoretical maximum yields and their oxygen requirements for a wide range of value-added products. Assessment of the process engineering challenges for methanol and ethylene glycol-based fermentations underscores the theoretical advantages of new synthetic metabolic routes and advocates greater consideration of ethylene glycol, a C2 substrate that has received comparatively little attention to date.

CO2 Activation over Nanoshaped CeO2 Decorated with Nickel for Low-Temperature Methane Dry Reforming

Dry reforming of methane (DRM) is a promising way to convert methane and carbon dioxide into H₂ and CO (syngas). CeO₂ nanorods, nanocubes, and nanospheres were decorated with 1-4 wt % Ni. The materials were structurally characterized using TEM and in situ XANES/EXAFS. The CO₂ activation was analyzed by DFT and temperature-programmed techniques combined with MS-DRIFTS. Synthesized CeO₂ morphologies expose {111} and {100} terminating facets, varying the strength of the CO₂ interaction and redox properties, which influence the CO₂ activation. Temperature-programmed CO₂ DRIFTS analysis revealed that under hydrogen-lean conditions mono- and bidentate carbonates are hydrogenated to formate intermediates, which decompose to H₂O and CO. In excess hydrogen, methane is the preferred reaction product. The CeO₂ cubes favor the formation of a polydentate carbonate species, which is an inert spectator during DRM at 500 °C. Polydentate covers a considerable fraction of ceria's surface, resulting in less-abundant surface sites for CO₂ dissociation.

Highly dispersed Ni-based catalysts derived from the LaNiO3 perovskite for dry methane reforming: promotional effect of the Ni0–Ni2+ dipole inlaid on the support

A hyperdispersed Ni-based catalyst from LaNiO3 performed well in dry methane reforming reaction, which was attributed to the promotional effect of the Ni0–Ni2+ dipole.

Nanowire-Based Materials as Coke-Resistant Catalyst Supports for Dry Methane Reforming

In this paper, nanowire-supported catalysts loaded with nickel are shown to be coke resistant compared to nanoparticle-supported catalysts. Specifically, Ni-loaded titania-based nanowire catalysts were tested with the dry methane reforming process in a laboratory-scale continuous packed-bed atmospheric reactor. The CO2 conversion rate stayed above 90% for over 30 h on stream under coke-promoting conditions, such as high flow rates, low temperatures, and a high ratio of CH4 to CO2. The coke (CxHy, x>>y) on the spent catalyst surface for both nanowire- and nanoparticle-supported catalysts was characterized by TGA, temperature-programmed reduction (TPR), and electron microscopy (SEM/TEM/EDS), and it was revealed that the types of carbon species present and their distribution over the morphology-enhanced materials played a major role in the deactivation. The CO2 conversion activity of Ni supported on titania nanoparticles was reduced from ~80% to less than 72% in 30 h due to the formation of a graphitic coke formation. On the other hand, Ni particles supported on nanowires exhibited cube-octahedral morphologies, with a high density of non- (111) surface sites responsible for the increased activity and reduced graphitic coke deposition, giving a sustained and stable catalytic activity during a long time-on-stream experiment.

Optimization of Synthesis Conditions of Ni/SBA-15 Catalysts: Confined Nanoparticles and Improved Stability in Dry Reforming of Methane

Despite its economic and environmental advantages, the dry reforming of methane using supported Ni-based catalysts remains challenging due to problems of metal particle sintering and carbon deposition, which lead to loss in catalytic activity. In this study, different silica supports, containing 5 wt% nickel, were prepared and characterized by N2 sorption, XRD, TPR, and TEM/SEM, in addition to Raman and TGA/MS for the spent catalysts. Different synthesis conditions were thus varied, like nickel deposition method, nature of nickel precursor salt, conditions for thermal activation, and nature of support. The results showed that enhanced metal dispersion, good confinement, and efficient stabilization of the active phase inside the pores can be achieved by using a well-structured mesoporous support. Moreover, it was demonstrated that carbon resistance can be improved when small nickel particles are well confined inside the pores. The strategies that affect the final dispersion of nickel particles, their consequent confinement inside (or deposition outside) the mesopores and the resulting catalytic activity and stability include mainly the application of hydrothermal treatment to the support, the variation of the nature of nickel precursor salt, and the conditions for thermal activation. General guidelines for the preparation of suitable Ni-based catalysts highly active and stable for dry reforming of methane (DRM) are thus presented in this work.

NiYAl-Derived Nanoporous Catalysts for Dry Reforming of Methane

Dry reforming of methane can be used for suppressing the rapid growth of greenhouse gas emissions. However, its practical implementation generally requires high temperatures. In this study, we report an optimal catalyst for low-temperature dry reforming of methane with high carbon coking resistance synthesized from NiYAl alloy. A facile two-step process consisting of preferential oxidation and leaching was utilized to produce structurally robust nanoporous Ni metal and Y oxides from NiYAl₄. The catalyst exhibited an optimal carbon balance (0.96) close to the ideal value of 1.0, indicating the optimized dry reforming pathway. This work proposes a facile route of the structural control of active metal/oxide sites for realizing highly active catalysts with long-term durability.

Hierarchical Fe-modified MgAl2O4 as a Ni-catalyst support for methane dry reforming

Hierarchical Fe-modified MgAl₂O₄ as a Ni-catalyst support with strong sintering resistance and anti-carbon ability for methane dry reforming.

Preparation of biomass-derived porous carbon supported Ni nanoparticles for CO2 reforming of CH4

A schematic diagram for the reaction of CH₄ and CO₂ over a Ni/bio-char catalyst.

Catalytic partial oxidation of methane to syngas over perovskite catalysts

Partial oxidation of methane (POM) significantly offers benefits to the industrial production of syngas in comparison with other conventional processes in terms of hydrogen (H2)/carbon monoxide (CO) ratio and degree of catalyst deactivation induced by carbonaceous species. Thus, the increasing concern on commercialisation of POM technology has driven the catalyst system to enter another stage of developing a novel catalyst, namely perovskite. POM is comprehensively reviewed and compared with various perovskite catalysts. Apart from studying process chemistry to understand POM reaction, the role of metal types for perovskite structure on catalytic performance and coke selectivity are also scrutinised and summarised. Additionally, the comprehension of POM pathways and the corresponding pictorial depiction are discussed and provided in this paper.

Nanoporous Nickel Composite Catalyst for the Dry Reforming of Methane

The development of efficient catalysts with high activities and durabilities for use in the dry reforming of methane (DRM) is desirable but challenging. We report the development of a nanoporous nickel composite (nanoporous Ni/Y₂O₃) via a facile one-step dealloying technique, for use in the DRM. Focusing on the low-temperature DRM, our composite possessed remarkable activity and durability against coking compared with conventional particle-based Ni catalysts. This was attributed to the aluminum oxides present on the Ni surface, which suppress pore coarsening. In addition, the inert bundled Y₂O₃ nanowires are suitable for use as substrates for nanoporous Ni.

Hierarchically Structured Porous Spinels via an Epoxide-Mediated Sol-Gel Process Accompanied by Polymerization-Induced Phase Separation

Enhancing the activity and stability of catalysts is a major challenge in scientific research nowadays. Previous studies showed that the generation of an additional pore system can influence the catalytic performance of porous catalysts regarding activity, selectivity, and stability. This study focuses on the epoxide-mediated sol-gel synthesis of mixed metal oxides, NiAl₂O₄ and CoAl₂O₄, with a spinel phase structure, a hierarchical pore structure, and Ni and Co contents of 3 to 33 mol % with respect to the total metal content. The sol-gel process is accompanied by a polymerization-induced phase separation to introduce an additional pore system. The obtained mixed metal oxides were characterized with regard to pore morphology, surface area, and formation of the spinel phase. The Brunauer-Emmett-Teller surface area ranges from 74 to 138 m²·g^-1 and 25 to 94 m²·g^-1 for Ni and Co, respectively. Diameters of the phase separation-based macropores were between 500 and 2000 nm, and the mesopore diameters were 10 nm for the Ni-based system and between 20 and 25 nm for the cobalt spinels. Furthermore, Ni-Al spinels with 4, 5, and 6 mol % Ni were investigated in the dry reforming of CH₄ (DRM) with CO₂ to produce H₂ and CO. CH₄ conversions near the thermodynamic equilibrium were observed depending on the Ni content and reaction temperature. The Ni catalysts were further compared to a noble metal-containing catalyst based on a spinel system showing comparable CH₄ conversion and carbon selectivity in the DRM.

Silica-based micro- and mesoporous catalysts for dry reforming of methane

With wide availability, high thermal stability and high specific surface area, silica-based micro- and mesoporous materials show promising performance for dry reforming of methane reaction, boosting efficient and sustainable utilization of greenhouse gases.

Mechanistic study of dry reforming of ethane by CO2 on a bimetallic PtNi(111) model surface

A combined DFT and KMC study pinpoints the origin of high selectivity toward syngas during CO₂ reduction by CH₃CH₃ on a PtNi model catalyst.

Sustainable Conversion of Carbon Dioxide: An Integrated Review of Catalysis and Life Cycle Assessment

CO₂ conversion covers a wide range of possible application areas from fuels to bulk and commodity chemicals and even to specialty products with biological activity such as pharmaceuticals. In the present review, we discuss selected examples in these areas in a combined analysis of the state-of-the-art of synthetic methodologies and processes with their life cycle assessment. Thereby, we attempted to assess the potential to reduce the environmental footprint in these application fields relative to the current petrochemical value chain. This analysis and discussion differs significantly from a viewpoint on CO₂ utilization as a measure for global CO₂ mitigation. Whereas the latter focuses on reducing the end-of-pipe problem "CO₂ emissions" from todays' industries, the approach taken here tries to identify opportunities by exploiting a novel feedstock that avoids the utilization of fossil resource in transition toward more sustainable future production. Thus, the motivation to develop CO₂-based chemistry does not depend primarily on the absolute amount of CO₂ emissions that can be remediated by a single technology. Rather, CO₂-based chemistry is stimulated by the significance of the relative improvement in carbon balance and other critical factors defining the environmental impact of chemical production in all relevant sectors in accord with the principles of green chemistry.

Investigation of mesoporous NiAl2O4/MOx (M = La, Ce, Ca, Mg)–γ-Al2O3 nanocomposites for dry reforming of methane

Mesoporous NiAl₂O₄/MO_x (M = La, Ce, Ca, Mg)–γ-Al₂O₃ composites through a one-pot partial hydrolysis method showed excellent catalytic performance for dry reforming of methane.

Simply packaging Ni nanoparticles inside SBA-15 channels by co-impregnation for dry reforming of methane

The highly dispersed Ni nanoparticles inside SBA-15 channels (Ni@SBA-15) were synthesized simply by co-impregnation using ethylene glycol (EG).

High sintering-/coke-resistance Ni@SiO2/Al2O3/FeCrAl-fiber catalyst for dry reforming of methane: one-step, macro-to-nano organization via cross-linking molecules

A thin-felt, microfibrous-structured Ni@SiO₂/Al₂O₃/FeCrAl-fiber catalyst was fabricated by one-step, top-down macro–micro–nano organization, displaying tremendous potential for dry reforming of methane.