In-situ tuning of catalytic activity by thermoelectric effect

For the first time, a new type of reactor which can combine thermoelectric energy harvesting and electrochemical promotion of catalysis was developed. A novel use of thermoelectric material as a catalyst support and promoter was investigated. A facile, cost-effective and scalable synthesis of thermoelectric material BiCuSeO has been developed. It was discovered that the catalytic activity of Pt supported on the thermoelectric material BiCuSeO, through the ethylene oxidation, can be increased by several tens to several hundreds of times by a thermoelectric voltage. We call this Thermoelectric Promotion of Catalysis (TEPOC). The catalytic activity under fuel-lean and fuel-rich conditions was also investigated for ethylene oxidation. It is believed that oxygen was more strongly and C₂H₄ was weakly adsorbed on the catalyst Pt surface under lean-fuel conditions (O₂/C₂H₄ > 1). However, under rich-fuel conditions (C₂H₄/O₂> 1.4), C₂H₄ became strongly adsorbed (probably chemisorbed) to the surface especially at a high Seebeck voltage, this blocked the catalyst surface, reduced the catalytic active site, hence the rate became smaller. To further investigate the TEPOC effect, the CO₂ hydrogenation over the same catalysts supported on the thermoelectric BiCuSeO was also studied and the results confirmed similar significant promotional effect. It also was found that a negative thermoelectric voltage shifted chemical equilibrium towards the reverse water gas shift (RWGS) reaction and CO selectivity. As a results, the CO₂ hydrogenation conversion reached 48.4% (CO₂:H₂ = 1:4) with 100% CO selectivity for Pt(80)/BCSO at 656 K, which was above the thermodynamic equilibrium conversion (TEC) under no Seebeck voltage without methanation. It was established a linear relationship between Ln(r) and –eV/kьT, where –eV/kьT is the ratio between the extra electrochemical energy induced by thermoelectric effect and the thermal energy of an electron. From this it was derived that the promotional effect was attributed to the change of work function of the catalyst surface, accompanied by charge transfer from the bulk to the surface due to the thermoelectric effect. ii The discovery of TEPOC prompts that many catalytic chemical reactions can be tuned in-situ and independently from the change of conditions within the reaction chamber, to achieve much higher reaction rate, or at lower temperature, or have better desired selectivity through changing the backside temperature of the thermoelectric catalyst support

Producing upgradeable bio-oil from food bio-waste via hybrid-assisted pretreatment coupled with catalytic hydrotreatment

Slurry\ua0food waste sourced from Renova (Gothenburg, Sweden) was investigated as a model for generating upgradeable bio-oil via a hybrid-assisted\ua0pretreatment\ua0along with a catalytic hydrotreatment process. Hybrid-assisted pretreatment has been examined for extracting and stabilizing of reactive-derived substances. For the resulting bio-crude and residual solids, the properties of the heteroatoms were also examined prior to the catalytic hydrotreatment experiments. Hybrid-assisted pretreatment is an interesting solution in that it maximizes the bio-crude yield and transfers significant amounts of the nitrogenous content (De-N ∼83.3\ua0%, dry basis) into the residual solids. Nearly 87\ua0wt% of the oxygenated\ua0monomers\ua0were found in the obtained bio-crude, which possessed 52.0\ua0wt% of alcohols. The highest upgradeable bio-oil of 86.0\ua0wt% was achieved during catalytic hydrotreatment of the bio-crude and residual solids jointly: producing blends of up to 78\ua0wt% of hydrocarbons, 14\ua0wt% oxygenated and <6\ua0wt% of cyclic, aromatics, N-containing components

Evaluation of kraft and hydrolysis lignin hydroconversion over unsupported NiMoS catalyst

Catalytic hydroconversion of Kraft and hydrolysis lignins was for the first time compared in a batch reactor over an unsupported NiMoS-SBA catalyst. We also report the effect of key reaction parameters on the yields and properties of the products. The results obtained at 20 wt% catalyst loading for hydrolysis lignin showed the highest monomer yield of 76.0 wt%, which consisted of 39 wt% aromatics with the lowest alkylphenolics yield of 10.1 wt%. Identical operating conditions, 400 \ub0C, 80 bar, 5 h at 10 wt% catalyst loading, were used to compare both lignins and the highest monomer yield (64.3 wt%) was found for the hydrolysis lignin, consisting of 16.0 wt% alkylphenolics and 20.1 wt% aromatic compounds. These values are considerably higher than those for Kraft lignin with its 47.0 wt% monomer yield. We suggest that the reason for high yields of monomeric units from hydrolysis lignin is that it is more reactive due to its lower ash and sulfur contents and the chemical structural differences compared to the Kraft lignin. More precisely, the bio-oil from hydrolysis lignin contained higher yields of small molecules, sourced from ring-opening of cellulose in the hydrolysis lignin, which could stabilize the reactive oligomeric groups. These yields were two to seven times higher from kraft and hydrolysis lignin, respectively, compared to those obtained without catalyst. The results showed that the NiMoS-SBA catalyst is a promising catalyst for reductive depolymerization of lignin and in addition that the regenerated catalyst had good stability for multiple reaction cycles

In-situ tuning of catalytic activity by thermoelectric effect for ethylene oxidation

Thermoelectric material BiCuSeO used as a support and promoter for catalytic ethylene oxidation is reported here. The catalytic activity on the continuous and non-continuous catalyst Pt supported on BiCuSeO was observed to be promoted in-situ by a thermoelectric Seebeck voltage generated by the temperature gradient across the material. It is also shown this thermoelectric promotion of catalysis enabled the thermoelectric material BiCuSeO itself to be highly catalytic active for ethylene oxidation. A good linear relationship between the logarithm of the reaction rate and the thermoelectric Seebeck voltage was observed. This thermoelectric promotion of catalysis is attributed to the change of work function of the catalyst surface, accompanied by a charge transfer from the bulk to the surface due to the thermoelectric effect

CO2 hydrogenation to light olefins using In2O3 and SSZ-13 catalyst − Understanding the role of zeolite acidity in olefin production

With the aim to explore the effect of acidic properties of zeolites in tandem catalysts on their performance for CO2 hydrogenation, two types of SSZ-13 zeolites with similar bulk composition, but different arrangements of framework Al, were prepared. Their morphology, pore structure, distribution of framework Al, surface acid strength and density, were explored. The results showed that SSZ-13 zeolites with isolated aluminum distribution could be successfully synthesized, however, they contained structural defects. During calcination, the framework underwent dealumination, resulting in weaker Br\uf8nsted acidity and lower crystallinity. The morphologies were, however, well preserved. Compared with the SSZ-13 zeolites, synthesized conventionally, these low acidity SSZ-13 zeolites with isolated aluminum were good zeolite components in bifunctional catalysts for CO2 hydrogenation to light olefins. By combining with In2O3, they exhibited better catalytic performance for light olefin production during CO2 hydrogenation at low temperatures. Na+ cation exchange was used to adjust the Br\uf8nsted acid site (BAS) density with only minor changes to the cavity structure. Comparative experiments established that the BAS density of the zeolite, rather than the framework Al distribution (BAS distribution), overwhelmingly affected catalyst stability and product selectivity. A higher acid density reduced the selectivity for light olefins, while lower acid density tended to form inert coke species leading to rapid deactivation. The ideal amount of BAS density in the bifunctional catalyst was approximately 0.25 mmol/g, which exhibited 70% selectivity for light olefins among hydrocarbons, and 74% selectivity for CO without deactivation, after 12 h reaction at 325 ℃ and 10 bar

Towards stable nickel catalysts for selective hydrogenation of biomass-based BHMF into THFDM

Selective transformation of BHMF (2,5-bis(hydroxymethyl)furan) to THFDM (tetrahydrofuran-2,5-dimethanol) over a variety of structured Ni/Sx-Z1−x catalysts was investigated. The effects of support, Ni loading, solvent, temperature, pressure, and particle size on the conversion and selectivity were studied. Among them, the 10 wt% Ni catalyst supported on the SiO2:ZrO2 weight ratio of 90:10 (10NiS90Z10) exhibits the best performance in terms of BHMF conversion and THFDM selectivity. Its good performance was attributed to its well-balanced properties, that depend upon the ZrO2 content of the support in combination with SiO2, the active Ni sites-support interaction, and acidity/basicity ratio of each catalyst resulting in different Ni dispersions. Importantly, the 10NiS90Z10 catalyst showed a stable selectivity to THFDM (>94%), with 99.4% conversion of BHMF during 2 h reaction time. Poor catalytic activity resulted from excessive ZrO2 content (>10 wt%). The structural, textural, and acidity properties of NiSi100−y-Zry catalysts, tuned by selectively varying the Ni amount from 5 to 15 wt%, were critically investigated using numerous material characterization techniques. Catalyst recycling experiments revealed that the catalyst could be recycled several times without any measurable loss of catalytic activity

Effect of DMSO on the catalytical production of 2,5-bis(hydoxymethyl)furan from 5-hydroxymethylfurfural over Ni/SiO2 catalysts

Hydroconversion of 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydoxymethyl)furan (BHMF) was studied over mono- and bimetallic supported catalysts. It was found that monometallic Ni/SiO2 catalysts exhibited superior performance with a total yield of BHMF of up to 99 wt%. This excellent performance may be attributed to higher Ni dispersion and low acidity of the support. Dimethyl sulfoxide (DMSO) is often present in HMF, due to the route used for its synthesis. DMSO adsorption caused a clear reduction of Ni/SiO2 performance for the HMF hydrodeoxygenation reaction. Characterization of the spent catalysts was performed using HAADF-STEM-EDX, Raman, ICP, and XPS spectroscopies, and showed the presence of sulfur and graphitic carbon, which could explain the deactivation

Insights into Photosensitized Reactions for Upgrading Lignin

The conversion of lignin into valuable chemical products is important for the shift away from the petrochemical industry toward a more sustainable system of biorefineries. However, the recalcitrance and heterogeneity of lignin have made its selective depolymerization a difficult task. Photochemical methods of lignin conversion are being investigated because of the potential to operate photoreactors at milder temperatures and pressures than thermal methods and to achieve efficient reaction pathways. Furthermore, light-driven reactions facilitate reaction pathways that cannot be accessed by conventional/thermal methods. Most of the current research focuses on photocatalytic methods, which are interesting due to their potentially high selectivity, but come with the disadvantage of catalyst costs and separation requirements. In this work, we continue our investigation into the use of ultraviolet light-emitting diodes, which aims to utilize the advantages of photochemistry, while avoiding the use of expensive catalysts. Photosensitizers can participate in energy transfer, electron transfer, and hydrogen abstraction in photochemical reactions. Here, we investigated the effects of a common photosensitizer, benzophenone, on the photochemical conversion of lignin, and 2-(benzyloxy)phenol (2BP), a compound with an ether bond between two aromatic units. We monitored the conversion reactions using complementary techniques of 1H nuclear magnetic resonance (NMR), diffusion NMR, and in situ Fourier transform infrared (FTIR) spectroscopy. For 2BP, the reactions with benzophenone progressed slower and without a difference in the final product formation. However, several differences were observed in photoreactions utilizing Kraft lignin and benzophenone compared to those without benzophenone. For example, a faster decay of the 1H NMR peak corresponding to aromatic/phenolic protons and different changes in the shape of methoxy peaks were observed, indicating the formation of different products. This work demonstrates that benzophenone participates in the photoreactions of Kraft lignin and that the photoreactions of Kraft lignin and 2BP are different. Depolymerization of lignin into smaller fragments was confirmed with diffusion NMR, both with and without the photosensitizer

Stabilization of bio-oil from simulated pyrolysis oil using sulfided NiMo/Al2O3 catalyst

Pyrolysis oil comprises compounds with a broad range of functional groups making its thermal/catalytic upgrading challenging due to the formation of undesired char. In this context, the current contribution addresses the thermal and catalytic hydrotreatment of a simulated pyrolysis oil containing all the representative groups of compounds under bio-oil stabilization conditions (180–300 \ub0C, 60 bar, 4 h) using sulfided NiMo/Al2O3. The effect of reaction conditions and different oxygenated organic compounds on the yields and properties of products was compared thoroughly. Interestingly, a correlation between the presence/absence of oxygenated furan and sugar compounds was found to significantly affect the yield of liquid product containing stabilized compounds. The presence of such compound groups significantly enhances the solid formation via oligomerization and polymerization reactions. To gain further insight, the solid products were analyzed/characterized in detail to elucidate their characteristics by extracting them into a dimethyl sulfoxide (DMSO) soluble and insoluble solid fraction. It was found that in the presence of NiMo/Al2O3, increasing temperature from 180 to 300 \ub0C enhances the formation of liquid product due to transformation of some of the soluble solids, while for experiments without the catalyst, the formation of solids was significantly higher. Oppositely, during heating up to 180 \ub0C, no solids were found in the case without the catalyst, however the presence of the catalyst during heating resulted in solid formation due to various catalytic reactions that promoted char formation. Analysis of solids revealed that the structure of soluble solids at lower temperatures (180 \ub0C) using the catalyst was closely related to sugar derivatives, whereas the corresponding insoluble solids with higher molecular weight were not fully char-like developed. However, at higher temperatures, the soluble and insoluble solid compositions were found to contain aliphatic compounds and fully developed char, respectively. Therefore, the stabilization of furan particularly with attached carbonyl groups and sugars derivatives in pyrolysis oil is of great importance to improve upgrading efficiency

Elucidating the role of NiMoS-USY during the hydrotreatment of Kraft lignin

Major hurdles in Kraft lignin valorization require selective cleavage of etheric and C–C linkages and subsequent stabilization of the fragments to suppress repolymerization reactions to yield higher monomeric fractions. In this regard, we report the development of efficient NiMo sulfides and ultra-stable Y zeolites for the reductive liquefaction and hydrodeoxygenation of Kraft lignin in a Parr autoclave reactor at 400 \ub0C and 35 bar of H2 (@25 \ub0C). Comparing the activity test without/with catalyst, it is revealed that NiMo sulfides over ultra-stable Y zeolites (silica/alumina = 30) achieved a significant reduction (∼50 %) of the re-polymerized solid residue fraction leading to a detectable liquid product yield of 30.5 wt% with a notable monocyclic and alkylbenzenes selectivity (∼61 wt%). A physical mixture counterpart, consisting of hydrothermally synthesized unsupported NiMoS and Y30, on the other hand, shows lower selectivity for such fractions but higher stabilization of the lignin fragments due to enhanced access to the active sites. Moreover, an extended reaction time with higher catalyst loading of the impregnated NiMoY30 facilitated a remarkable alkylbenzene (72 wt%) selectivity with an increased liquid yield of 38.9 wt% and a reduced solid residue of 16.4 wt%. The reason for the high yield and selectivity over NiMoY30, according to the catalyst characterization (H2-TPR, XPS, TEM) can be ascribed to enhanced stabilization of depolymerized fragments via H2-activation at a lower temperature and high hydrodeoxygenation ability. In addition, the better proximity of the acidic and deoxygenation sites in NiMoY30 was beneficial for suppressing the formation of polycyclic aromatics