State of art and perspectives about the production of methanol, dimethyl ether and syngas by carbon dioxide hydrogenation

Off-design operation of super critical CO2 cycle integrated with reciprocating engine

This paper presents the results of simulations of a supercritical CO2 system integrated with a 180 kW nominal power piston engine. The sCO2 system consists of a compressor, expander, and four heat exchangers. The analysis delivered the optimum operating point of the system, where the sCO2 system generates an extra 18.03 kW. The main research was oriented into generation of off-design characteristics of the system, where sCO2 system were subjected to varying engine load and the system response was analyzed. The results of the calculations refer to the nominal point of the system and are given as maps of parameter changes normalized to the nominal point. The supercritical CO2 system itself is not controlled (only the speed of the turbomachinery is kept constant), while the power of this system depends on the current state of the reciprocating engine and directly influences the amount and temperature of the exhaust gases fed to the heater. The study revealed that the sCO2-biogas piston engine hybrid system would benefit from extra power generated by sCO2 when the engine operates with at least 60 % of its nominal power.

CO2 Hydrogenation on Carbides Formed in situ on Carbon-Supported Iron-Based Catalysts in High-Density Supercritical Medium

CO2 conversion via hydrogenation over iron-based catalysts on non-carbon supports produces mainly CO or methane by the Sabatier reaction, while the formation of C2+ hydrocarbons is of greatest interest. CxHy production from CO2 may be considered as a two-step process with the initial formation of carbon monoxide by the reverse water gas shift reaction followed by the Fischer-Tropsch synthesis (FTS). In the present work CO2 hydrogenation over iron-based catalysts (Fe, FeCr, FeK) deposited on a carbon carrier has been studied. The catalyst structure has been investigated by XRD, TEM, XPS, Mössbauer spectroscopy and in situ magnetometry. Spinel-type oxide phases (magnetite Fe3O4; maggemite γ-Fe2O3, and, in the case of FeCr/C catalyst, iron chromite Fe1+xCr2-xO4) are formed on the catalysts, and they contribute exclusively to the CO production. Iron carbides, active in FTS, are formed on Fe- and FeK-catalysts during pre-activation in reducing environment and then during the reaction. The reaction over the 20Fe1K/C catalyst in supercritical high-density CO2/H2 substrate (400 °C, 8.5 MPa) leads to 72 % selectivity for C1-C12+ hydrocarbons (alkanes and alkenes). Under the same conditions, iron carbides do not form on the FeCr/C catalysts, and CO2 hydrogenation results in the CO formation with the selectivity of 90-100 %.

Achieving efficient almost CO-free hydrogen production from methanol steam reforming on Cu modified α-MoC

Methanol, serving as a hydrogen carrier, is utilized for hydrogen production through steam reforming, a promising technology for on-vehicle hydrogen applications. Despite the impressive performance of noble-metal catalysts in hydrogen generation, the development of highly efficient non-noble-metal heterogeneous catalysts remains a formidable challenge. In our investigation, we systematically controlled the influence of the MoC phase on the dispersion of active copper metal to enhance the catalytic performance of methanol steam reforming (MSR). Within the Cu/MoC catalyst systems, featuring MoC phases including α-MoC1-x and Mo2C phases, alongside MoO2 phases, the Cu/α-MoC catalyst exhibited exceptional catalytic efficacy at 350 °C. It achieved a remarkable hydrogen selectivity of up to 80% and an outstanding CO selectivity of 0. Notably, its hydrogen production rate reached 44.07 mmol gcat-1 h-1, surpassing that of Cu/Mo2C (37.05 mmol gcat-1 h-1), Cu/MoO2 (19.02 mmol gcat-1 h-1), and commercial CuZnAl (38 mmol gcat-1 h-1) catalysts. Additionally, we introduced the concept of the (Cu1-Cun)/α-MoC catalyst, wherein Cu atoms are immobilized on the α-MoC surface, facilitating the coexistence of isolated Cu atoms (Cu1) and subnanometer copper cluster (Cun) species at a high dispersibility. This innovative design capitalizes on the robust interaction between the α-MoC1-x phase and the Cu active center, yielding a substantial augmentation in the catalytic activity.

Achieving artificial carbon cycle via integrated system of high-emitting industries and CCU technology: Case of China

Process-related carbon emissions, which cannot be completely eliminated by the improvement of processes and energy structure, are recognized as an enormous challenge for in-depth decarbonization. To accelerate the achievement of carbon neutrality, the concept of 'artificial carbon cycle' is proposed based on the integrated system of process-related carbon emissions from high-emitting industries and CCU technology as a potential pathway towards a sustainable future. This paper conducts a systematic review on the integrated system with the case of China, which is the largest carbon-emitting and manufacturing country, to provide a clearer and more meaningful analysis. Multi-index assessment was used to organize the literature and draw the useful conclusion. Based on literature review, the high-quality carbon sources, reasonable carbon capture approaches and promising chemical products were identified and analyzed. Then the potential and practicability of the integrated system was further summarized and analyzed. Finally, key factors of future development including technology improvement, green hydrogen, clean energy and industrial cooperation were stressed to provide a theoretical reference for future researchers and policy makers.

Solution-processable polymers of intrinsic microporosity for gas-phase carbon dioxide photoreduction

Four solution-processable, linear conjugated polymers of intrinsic porosity are synthesised and tested for gas phase carbon dioxide photoreduction. The polymers' photoreduction efficiency is investigated as a function of their porosity, optical properties, energy levels and photoluminescence. All polymers successfully form carbon monoxide as the main product, without the addition of metal co-catalysts. The best performing single component polymer yields a rate of 66 μmol h^-1 m^-2, which we attribute to the polymer exhibiting macroporosity and the longest exciton lifetimes. The addition of copper iodide, as a source of a copper co-catalyst in the polymers shows an increase in rate, with the best performing polymer achieving a rate of 175 μmol h^-1 m^-2. The polymers are active for over 100 h under operating conditions. This work shows the potential of processable polymers of intrinsic porosity for use in the gas phase photoreduction of carbon dioxide towards solar fuels.

Advanced zeolite and ordered mesoporous silica-based catalysts for the conversion of CO2 to chemicals and fuels

For many years, capturing, storing or sequestering CO₂ from concentrated emission sources or from air has been a powerful technique for reducing atmospheric CO₂. Moreover, the use of CO₂ as a C1 building block to mitigate CO₂ emissions and, at the same time, produce sustainable chemicals or fuels is a challenging and promising alternative to meet global demand for chemicals and energy. Hence, the chemical incorporation and conversion of CO₂ into valuable chemicals has received much attention in the last decade, since CO₂ is an abundant, inexpensive, nontoxic, nonflammable, and renewable one-carbon building block. Nevertheless, CO₂ is the most oxidized form of carbon, thermodynamically the most stable form and kinetically inert. Consequently, the chemical conversion of CO₂ requires highly reactive, rich-energy substrates, highly stable products to be formed or harder reaction conditions. The use of catalysts constitutes an important tool in the development of sustainable chemistry, since catalysts increase the rate of the reaction without modifying the overall standard Gibbs energy in the reaction. Therefore, special attention has been paid to catalysis, and in particular to heterogeneous catalysis because of its environmentally friendly and recyclable nature attributed to simple separation and recovery, as well as its applicability to continuous reactor operations. Focusing on heterogeneous catalysts, we decided to center on zeolite and ordered mesoporous materials due to their high thermal and chemical stability and versatility, which make them good candidates for the design and development of catalysts for CO₂ conversion. In the present review, we analyze the state of the art in the last 25 years and the potential opportunities for using zeolite and OMS (ordered mesoporous silica) based materials to convert CO₂ into valuable chemicals essential for our daily lives and fuels, and to pave the way towards reducing carbon footprint. In this review, we have compiled, to the best of our knowledge, the different reactions involving catalysts based on zeolites and OMS to convert CO₂ into cyclic and dialkyl carbonates, acyclic carbamates, 2-oxazolidones, carboxylic acids, methanol, dimethylether, methane, higher alcohols (C₂₊OH), C₂₊ (gasoline, olefins and aromatics), syngas (RWGS, dry reforming of methane and alcohols), olefins (oxidative dehydrogenation of alkanes) and simple fuels by photoreduction. The use of advanced zeolite and OMS-based materials, and the development of new processes and technologies should provide a new impulse to boost the conversion of CO₂ into chemicals and fuels.

Role of Zr loading into In2O3 catalysts for the direct conversion of CO2/CO mixtures into light olefins

The effect of the ZrO₂ content on the performance (activity, selectivity, stability) of In₂O₃-ZrO₂ catalyst has been studied on the hydrogenation of CO₂/CO mixtures. This effect is a key feature for the viability of using In₂O₃-ZrO₂/SAPO-34 tandem catalysts for the direct conversion of CO₂ and syngas into olefins via oxygenates as intermediates. The interest of co-feeding syngas together with CO₂ resides in jointly valorizing syngas derived from biomass or wastes (via gasification) and supplying the required H₂. The experiments of methanol synthesis and direct synthesis of olefins, with In₂O₃-ZrO₂ and In₂O₃-ZrO₂/SAPO-34 catalysts, respectively, have been carried out under the appropriate conditions for the direct olefins synthesis (400 °C, 30 bar, H₂/CO_X ratio = 3) in an isothermal fixed bed reactor at low space time values (kinetic conditions) to evaluate the behavior and deactivation of the catalysts. The Zr/In ratio of 1/2 favors the conversion of CO₂ and CO_X, attaining good oxygenates selectivity, and prevents the sintering attributable to the over-reduction of the In₂O₃ (more significant for syngas feeds). The improvement is more remarkable in the direct olefins synthesis, where the thermodynamic equilibrium of methanol formation is displaced, and methanation suppressed (in a greater extent for feeds with high CO content). With the In₂O₃-ZrO₂/SAPO-34 tandem catalysts, the conversion of CO_x almost 5 folds respect oxygenates synthesis with In₂O₃-ZrO₂ catalyst, meaning the yield of the target products boosts from ∼0.5% of oxygenates to >3% of olefins (selectivity >70%) for mixtures of CO₂/CO_X of 0.5, where an optimum performance has been obtained.

Techno-economic and environmental assessments for sustainable bio-methanol production as landfill gas valorization

With the regular increase in global solid waste, landfilling is intensively used for waste disposal. However, landfill gas (LFG) produced as a byproduct during waste decomposition in the landfills is a serious problem since it leads to damage to the eco-systems. Accordingly, it has been highlighted to convert LFG into other value-added chemicals. In this study, LFG utilization was studied in terms of conversion into methanol (MeOH) by considering different scenarios of LFG utilization. Techno-economic analysis and environmental assessment were performed to identify the economic feasibility and environmental impact of each case. From the economic analysis, bio-MeOH production costs of 879.16, 724.52, and 1,130.74 $ ton^-1 for case 1, 2, and 3 was estimated with the economic infeasibility, while substantial cost reduction through projected cost analysis can lead to economic competitiveness (449.52 $ ton^-1 for case 2 and 595.76 $ ton^-1 for case 3). In sequence, the quantitative environmental impacts in terms of climate change impact were 2.360, 0.835, and 0.605 kg CO₂-eq kg MeOH^-1 for cases 1, 2, and 3, respectively. Based on the results of two analyses, a multi-criteria decision analysis was conducted to investigate the acceptable case of bio-MeOH production in the economic and environmental aspects. It can be concluded that the most feasible case depends on decision-makers if only economic and environmental criteria were considered. Therefore, dry reforming and membrane separation of LFG have considerable potential for bio-MeOH production in terms of LFG utilization for high weighting of economic and environmental aspects, respectively.

On the Effect of Cobalt Promotion over Ni/CeO2 Catalyst for CO2 Thermal and Plasma Assisted Methanation

In recent years, carbon dioxide hydrogenation leading to synthetic fuels and value-added molecules has been proposed as a promising technology for stabilizing anthropogenic greenhouse gas emissions. Methanation or Sabatier are possible reactions to valorize the CO2. In the present work, thermal CO2 methanation and non-thermal plasma (NTP)-assisted CO2 methanation was performed over 15Ni/CeO2 promoted with 1 and 5 wt% of cobalt. The promotion effect of cobalt is proven both for plasma and thermal reaction and can mostly be linked with the basic properties of the materials.

Capture and Reuse of Carbon Dioxide (CO2) for a Plastics Circular Economy: A Review

Plastic production has been increasing at enormous rates. Particularly, the socioenvironmental problems resulting from the linear economy model have been widely discussed, especially regarding plastic pieces intended for single use and disposed improperly in the environment. Nonetheless, greenhouse gas emissions caused by inappropriate disposal or recycling and by the many production stages have not been discussed thoroughly. Regarding the manufacturing processes, carbon dioxide is produced mainly through heating of process streams and intrinsic chemical transformations, explaining why first-generation petrochemical industries are among the top five most greenhouse gas (GHG)-polluting businesses. Consequently, the plastics market must pursue full integration with the circular economy approach, promoting the simultaneous recycling of plastic wastes and sequestration and reuse of CO2 through carbon capture and utilization (CCU) strategies, which can be employed for the manufacture of olefins (among other process streams) and reduction of fossil-fuel demands and environmental impacts. Considering the previous remarks, the present manuscript’s purpose is to provide a review regarding CO2 emissions, capture, and utilization in the plastics industry. A detailed bibliometric review of both the scientific and the patent literature available is presented, including the description of key players and critical discussions and suggestions about the main technologies. As shown throughout the text, the number of documents has grown steadily, illustrating the increasing importance of CCU strategies in the field of plastics manufacture.

Supply chain optimization framework for CO2 capture, utilization, and storage in Germany

In this study, the carbon capture, utilization, and sequestration (CCUS) supply chain network with real geographic locations of sources and sinks, and different CO2-based products for Germany is proposed here for the first time, because not yet investigated in the literature. The CCUS network is a large-scale comprehensive model which is used to meet the mandated target of CO2 emission reduction at different levels with a maximum profit. The novel CCUS infrastructure includes various stationary sources, capture processes, transportation modes, and sequestration and utilization sites. The results suggest that it is possible to reduce current CO2 emissions by 40–80% in Germany with the total annual costs ranging from 519.34 to 1372.03 billion euro while generating 681.55 to 1880.98 billion euro of revenue annually as a result of producing CO2-based chemical products including methanol, dimethyl ether, formic acid, acetic acid, urea, and polypropylene carbonate. Overall, the optimal CCUS systems achieve economic profits of 999.62–1568.17 euro per ton of CO2 captured and utilized. The CCUS model may be critical in aiding decision-makers to ascertain investment strategies for designing CCUS infrastructures.

Gallium nitride catalyzed the direct hydrogenation of carbon dioxide to dimethyl ether as primary product

The selective hydrogenation of CO₂ to value-added chemicals is attractive but still challenged by the high-performance catalyst. In this work, we report that gallium nitride (GaN) catalyzes the direct hydrogenation of CO₂ to dimethyl ether (DME) with a CO-free selectivity of about 80%. The activity of GaN for the hydrogenation of CO₂ is much higher than that for the hydrogenation of CO although the product distribution is very similar. The steady-state and transient experimental results, spectroscopic studies, and density functional theory calculations rigorously reveal that DME is produced as the primary product via the methyl and formate intermediates, which are formed over different planes of GaN with similar activation energies. This essentially differs from the traditional DME synthesis via the methanol intermediate over a hybrid catalyst. The present work offers a different catalyst capable of the direct hydrogenation of CO₂ to DME and thus enriches the chemistry for CO₂ transformations.

The conversion of CO₂ to valuable chemicals is still challenged by catalyst developments. Herein, the authors found that GaN is an efficient catalyst for selective CO₂ hydrogenation to dimethyl ether as the primary product, in contrast to the traditional methanol-intermediate route over hybrid catalysts.

Effect of Anode Material on Electrochemical Oxidation of Low Molecular Weight Alcohols-A Review

The growing climate crisis inspires one of the greatest challenges of the 21st century-developing novel power sources. One of the concepts that offer clean, non-fossil electricity production is fuel cells, especially when the role of fuel is played by simple organic molecules, such as low molecular weight alcohols. The greatest drawback of this technology is the lack of electrocatalytic materials that would enhance reaction kinetics and good stability under process conditions. Currently, electrodes for direct alcohol fuel cells (DAFCs) are mainly based on platinum, which not only provides a poor reaction rate but also readily deactivates because of poisoning by reaction products. Because of these disadvantages, many researchers have focused on developing novel electrode materials with electrocatalytic properties towards the oxidation of simple alcohols, such as methanol, ethanol, ethylene glycol or propanol. This paper presents the development of electrode materials and addresses future challenges that still need to be overcome before direct alcohol fuel cells can be commercialized.

Novel Heterogeneous Catalysts for CO2 Hydrogenation to Liquid Fuels

Carbon dioxide (CO₂) hydrogenation to liquid fuels including gasoline, jet fuel, diesel, methanol, ethanol, and other higher alcohols via heterogeneous catalysis, using renewable energy, not only effectively alleviates environmental problems caused by massive CO₂ emissions, but also reduces our excessive dependence on fossil fuels. In this Outlook, we review the latest development in the design of novel and very promising heterogeneous catalysts for direct CO₂ hydrogenation to methanol, liquid hydrocarbons, and higher alcohols. Compared with methanol production, the synthesis of products with two or more carbons (C₂₊) faces greater challenges. Highly efficient synthesis of C₂₊ products from CO₂ hydrogenation can be achieved by a reaction coupling strategy that first converts CO₂ to carbon monoxide or methanol and then conducts a C-C coupling reaction over a bifunctional/multifunctional catalyst. Apart from the catalytic performance, unique catalyst design ideas, and structure-performance relationship, we also discuss current challenges in catalyst development and perspectives for industrial applications.

Gas phase methanol synthesis with Raman spectroscopy for gas composition monitoring

Applicability of Raman spectroscopy for time-resolved gas composition monitoring during direct methanol synthesis via carbon dioxide hydrogenation was investigated. A series of methanol synthesis experiments with varied reactor conditions was conducted and the reactor outlet stream was analyzed with in-line gas Raman spectroscopy. Concentrations of H₂, CO₂ and CO were determined directly from the acquired spectral data. For evaluation of methanol and water content a data reconciliation algorithm was developed. The algorithm involves estimation of the occurring chemical reactions' extents by iterative minimization of the difference between concentration values acquired from the experimental data and concentration values computed based on the mass conservation principle. The obtained experimental concentrations were compared and validated against the results of the reactor mathematical modeling, which is based upon a well-established kinetic interpretation of the process. The findings indicate good repeatability and accuracy of the developed gas analysis system, which together with the advantageous temporal resolution of the method, make Raman spectroscopy a promising technique for fast response monitoring of the process.

Applicability of Raman spectroscopy for time-resolved gas composition monitoring during direct methanol synthesis via carbon dioxide hydrogenation is investigated.

Analysis of Research Status of CO2 Conversion Technology Based on Bibliometrics

The concentration of carbon dioxide in the air has risen sharply due to the use of fossil fuels, causing environmental problems such as the greenhouse effect, which seriously threatens humans’ living environment. Reducing carbon dioxide emissions while addressing energy shortages requires the conversion of CO2 into high added-value products. In this paper, the status of CO2 conversion research in the past ten years is analyzed using the bibliometric method; the influence of countries and institutions, journal article statistics and other aspects are statistically analyzed, and the research status of carbon dioxide catalytic conversion is briefly introduced. Finally, according to the analysis results and the existing problems of CO2 catalytic conversion research, the future development direction of CO2 catalytic conversion research is prospected.

Rh-induced Support Transformation and Rh Incorporation in Titanate Structures and Their Influence on Catalytic Activity

Rh is one of the most effective metals in several technologically important heterogeneous catalytic reactions, like the hydrogenation of CO2, and CO, the CO+H2O reaction, and methane and ethanol transformations. Titania and titanates are among the most frequently studied supports for Rh nanoparticles. The present study demonstrates that the nature of the support has a marked influence on the specific activity. For comparison, the catalytic activity of TiO2 P25 is also presented. It is pointed out that a certain amount of Rh can be stabilized as cation (Rh+) in ion-exchange positions (i.e., in atomic scale distribution) of the titanate framework. This ionic form does not exists on TiO2. We pay distinguished attention not only to the electronic interaction between Rh metal and the titania/titanate support, but also to the Rh-induced phase transitions of one-dimensional titanate nanowires (TiONW) and nanotubes (TiONT). Support transformation phenomena can be observed in Rh-loaded titanates. Rh decorated nanowires transform into the TiO2(B) phase, whereas their pristine counterparts recrystallize into anatase. The formation of anatase is dominant during the thermal annealing process in both acid-treated and Rh-decorated nanotubes; Rh catalysis this transformation. We demonstrate that the phase transformations and the formation of Rh nanoclusters and incorporated Rh ions affect the conversion and the selectivity of the reactions. The following initial activity order was found in the CO2 + H2, CO + H2O and C2H5OH decomposition reactions: Rh/TiO2 (Degussa P25) ≥ Rh/TiONW > Rh/TiONT. On the other hand it is remarkable that the hydrogen selectivity in ethanol decomposition was two times higher on Rh/TiONW and Rh/TiO(NT) catalysts than on Rh/TiO2 due to the presence of Rh+ cations incorporated into the framework of the titanate structures.

Green Synthetic Fuels: Renewable Routes for the Conversion of Non-Fossil Feedstocks into Gaseous Fuels and Their End Uses

Innovative renewable routes are potentially able to sustain the transition to a decarbonized energy economy. Green synthetic fuels, including hydrogen and natural gas, are considered viable alternatives to fossil fuels. Indeed, they play a fundamental role in those sectors that are difficult to electrify (e.g., road mobility or high-heat industrial processes), are capable of mitigating problems related to flexibility and instantaneous balance of the electric grid, are suitable for large-size and long-term storage and can be transported through the gas network. This article is an overview of the overall supply chain, including production, transport, storage and end uses. Available fuel conversion technologies use renewable energy for the catalytic conversion of non-fossil feedstocks into hydrogen and syngas. We will show how relevant technologies involve thermochemical, electrochemical and photochemical processes. The syngas quality can be improved by catalytic CO and CO2 methanation reactions for the generation of synthetic natural gas. Finally, the produced gaseous fuels could follow several pathways for transport and lead to different final uses. Therefore, storage alternatives and gas interchangeability requirements for the safe injection of green fuels in the natural gas network and fuel cells are outlined. Nevertheless, the effects of gas quality on combustion emissions and safety are considered.

Improving synthetic methylotrophy via dynamic formaldehyde regulation of pentose phosphate pathway genes and redox perturbation

Escherichia coli is an ideal choice for constructing synthetic methylotrophs capable of utilizing the non-native substrate methanol as a carbon and energy source. All current E. coli-based synthetic methylotrophs require co-substrates. They display variable levels of methanol-carbon incorporation due to a lack of native regulatory control of biosynthetic pathways, as E. coli does not recognize methanol as a proper substrate despite its ability to catabolize it. Here, using the E. coli formaldehyde-inducible promoter P_frm, we implement dynamic expression control of select pentose-phosphate genes in response to the formaldehyde produced upon methanol oxidation. Genes under P_frm control exhibited 8- to 30-fold transcriptional upregulation during growth on methanol. Formaldehyde-induced episomal expression of the B. methanolicus rpe and tkt genes involved in the regeneration of ribulose 5-phosphate required for formaldehyde fixation led to significantly improved methanol assimilation into intracellular metabolites, including a 2-fold increase of ¹³C-methanol into glutamate. Using a simple strategy for redox perturbation by deleting the E. coli NAD-dependent malate dehydrogenase gene maldh, we demonstrate 5-fold improved biomass formation of cells growing on methanol in the presence of a small concentration of yeast extract. Further improvements in methanol utilization are achieved via adaptive laboratory evolution and heterologous rpe and tkt expression. A short-term in vivo¹³C-methanol labeling assay was used to determine methanol assimilation activity for Δmaldh strains, and demonstrated dramatically higher labeling in intracellular metabolites, including a 6-fold and 1.8-fold increase in glycine labeling for the rpe/tkt and evolved strains, respectively. The combination of formaldehyde-controlled pentose phosphate pathway expression and redox perturbation with the maldh knock-out greatly improved both growth benefit with methanol and methanol carbon incorporation into intracellular metabolites.

The Effect of CeO2 Preparation Method on the Carbon Pathways in the Dry Reforming of Methane on Ni/CeO2 Studied by Transient Techniques

The present work discusses the effect of CeO2 synthesis method (thermal decomposition (TD), precipitation (PT), hydrothermal (HT), and sol-gel (SG)) on the carbon pathways of dry reforming of methane with carbon dioxide (DRM) applied at 750 °C over 5 wt% Ni/CeO2. In particular, specific transient and isotopic experiments (use of 13CO, 13CO2, and 18O2) were designed and conducted in an attempt at providing insights about the effect of support’s preparation method on the concentration (mg gcat−1), reactivity towards oxygen, and transient evolution rates (μmol gcat−1 s−1) of the inactive carbon formed under (i) CH4/He (methane decomposition), (ii) CO/He (reverse Boudouard reaction), and (iii) the copresence of the two (CH4/CO/He, use of 13CO). Moreover, important information regarding the relative contribution of CH4 and CO2 activation routes towards carbon formation under DRM reaction conditions was derived by using isotopically labelled 13CO2 in the feed gas stream. Of interest was also the amount, and the transient rate, of carbon removal via the participation of support’s labile active oxygen species.

Alcohol Synthesis from CO2 , H2 , and Olefins over Alkali-Promoted Au Catalysts-A Catalytic and In situ FTIR Spectroscopic Study

Au/TiO₂ and Au/SiO₂ catalysts containing 2 wt % Au and different amounts of K or Cs were tested for alcohol synthesis from CO₂ , H₂ , and C₂ H₄ /C₃ H₆ . 1-Propanol or 1-butanol/isobutanol were obtained in the presence of C₂ H₄ or C₃ H₆ . Higher yields of the corresponding alcohols were obtained over TiO₂ -based catalysts in comparison with their SiO₂ -based counterparts. This is caused by an enhanced ability of the TiO₂ -based catalysts for CO₂ activation, as concluded from in situ fourier-transform infrared (FTIR) spectroscopy and temporal analysis of products (TAP) studies. The synthesized carbonate and formate species adsorbed on the support do not hamper CO₂ conversion into CO and the hydroformylation reaction. The transformation of Au^δ+ to active Au⁰ sites proceeds during an activation procedure. As reflected by CO adsorption and scanning transmission electron microscopy, the accessible Au⁰ sites are influenced by the amount of alkali dopants and the support. FTIR data and TAP tests reveal a very weak interaction of C₂ H₄ with the catalyst, suggesting its quick reaction with CO and H₂ after activation on Au⁰ sites to form propanol and propane.