Temperature-induced modifications in natural zeolite clinoptilolite: effects on acidity and catalytic acetalization

This study delves into the acid modification of natural zeolite clinoptilolite, focusing on the identification of acid site types and their catalytic activity in the Brønsted acid-catalyzed acetalization of benzaldehyde with 1,3-butanediol. Following calcination, the samples underwent acidification via ammonium-ion exchange, resulting in approximately 45 % of the clinoptilolite cations being exchanged with ammonium ions. The investigation evaluates the structural, morphological, and textural alterations induced by this modification using XRD, FTIR, and nitrogen adsorption-desorption measurements. Ammonia-temperature-programmed desorption (NH3-TPD) analysis confirms the presence of medium to strong acidic protons, highlighting the acidity of the modified samples. Employing 27Al and 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy elucidated changes in the state and coordination of aluminum post-sample activation. Specifically, the 27Al MAS NMR spectra indicate a partial dealumination, evidenced by the emergence of 5 and 6-fold coordinated aluminum. Moreover, 29Si MAS NMR measurements tracked variations in the Si/Al ratio. The study probes the nature of these sites, their influence on catalytic activity, and the synergistic interplay between Brønsted acid sites and 5-fold coordinated aluminum. The results showcase that the prepared acidic natural clinoptilolite catalysts augment acidity and porosity, fostering promising implications for catalytic applications.<br/

Facile Synthesis and Life Cycle Assessment of Highly Active Magnetic Sorbent Composite Derived from Mixed Plastic and Biomass Waste for Water Remediation

[Image: see text] Plastic and biomass waste pose a serious environmental risk; thus, herein, we mixed biomass waste with plastic bottle waste (PET) to produce char composite materials for producing a magnetic char composite for better separation when used in water treatment applications. This study also calculated the life cycle environmental impacts of the preparation of adsorbent material for 11 different indicator categories. For 1 functional unit (1 kg of pomace leaves as feedstock), abiotic depletion of fossil fuels and global warming potential were quantified as 7.17 MJ and 0.63 kg CO(2) equiv for production of magnetic char composite materials. The magnetic char composite material (MPBC) was then used to remove crystal violet dye from its aqueous solution under various operational parameters. The kinetics and isotherm statistical theories showed that the sorption of CV dye onto MPBC was governed by pseudo-second-order, and Langmuir models, respectively. The quantitative assessment of sorption capacity clarifies that the produced MPBC exhibited an admirable ability of 256.41 mg g(–1). Meanwhile, the recyclability of 92.4% of MPBC was demonstrated after 5 adsorption/desorption cycles. Findings from this study will inspire more sustainable and cost-effective production of magnetic sorbents, including those derived from combined plastic and biomass waste streams

Performance Study of Methane Dry Reforming on Ni/ZrO₂ Catalyst

Dry reforming of methane (DRM) has important and positive environmental and industrial impacts, as it consumes two of the top greenhouse gases in order to produce syngas (H2 and CO) and thus hydrogen (H2). The performance of DRM of conversions of CH4 and CO2 was investigated over Ni/ZrO2 catalysts. The catalytic performance of all prepared catalysts for DRM was assessed in a micro-tubular fixed bed reactor under similar reaction conditions (i.e., activation and reaction temperatures at 700 °C, a feed flow rate of 70 mL/min, reaction temperature, and a 440 min reaction time). Various characterization techniques, such as BET, CO2-TPD, TGA, XRD, EDX, and TEM, were employed. The zirconia support was modified with MgO or Y2O3. The yttria-stabilized zirconia catalyst (5Ni15YZr) provided the optimum activity performance of CH4 and CO2 conversions of 56.1 and 64.3%, respectively, at 700 °C and a 70 mL/min flow rate; this catalyst also had the highest basicity. The Ni-based catalyst was promoted with Cs, Ga, and Sr. The Sr-promoted catalyst produced the highest enhancement of activity. The influence of the reaction temperature and the feed flow rate on 5Ni15YZr and 5NiSr15YZr indicated that the activity increased with the increase in the reaction temperature and lower feed flow rate. For 5Ni3Sr15YZr, at a reaction temperature of 800 °C, the CH4 and CO2 conversions were 76.3 and 79.9%, respectively, whereas at 700 °C, the conversions of CH4 and CO2 were 66.6 and 79.6% respectively

Predicting nickel catalyst deactivation in biogas steam and dry reforming for hydrogen production using machine learning

This study employs Random Forests (RF) and Artificial Neural Networks (ANN) to model the transient behavior of Ni catalyst deactivation during steam and dry reforming of model biogas containing H2S, with a focus on hydrogen production. Deactivation, induced by carbon deposition and sulfur poisoning, is a complex and transient phenomenon demanding precise kinetic mechanisms for accurately predicting Ni catalyst behavior in biogas reforming. Black-box machine learning (ML) models are developed, incorporating catalyst properties, biogas composition, and operating conditions. Encompassing both dry and steam reforming, the ML models aim to predict catalyst behavior, expressed in terms of packed bed reactor exit mole fractions (H2, CO, CH4, and CO2)and conversions (CH4 and CO2). The ML models are trained and tested across a temperature range of 700–900 C with 0–145 ppm of H2S in model biogas (CH4/CO2 ratio varying from 1.0 to 2.0). RF outperforms the ANN across all performance metrics, including overall R2 and root mean squared error (RMSE). The RF achieves a mean overall R2 of 0.979, with training and testing RMSE equal to 6.7 × 10−3 and 1.47 × 10−2 respectively. In contrast, the ANN achieves a mean overall R2 of 0.939, with training and testing RMSE equal to 2.6 × 10−2 and 2.55 ×10−2 respectively. Moreover, pre-trained RF models are validated with unseen data of dry reforming of biogas containing 30 ppm of H2S (25 data points). It is suggested that 35 % of this unseen experimental data is required to train the RF model for it to predict catalyst deactivation, achieving a validation R sufficiently2 &gt; 0.9. The mean overall R2 values attained by the RF fine-tuned on 35 % of the unseen experiment data for both CH4 and CO2 conversions, as well as for all mole fraction predictions, are 0.952 and 0.948, respectively

Lanthanum–Cerium-Modified Nickel Catalysts for Dry Reforming of Methane

The catalyst MNi0.9Zr0.1O3 (M = La, Ce, and Cs) was prepared using the sol–gel preparation technique investigated for the dry reforming of methane reaction to examine activity, stability, and H2/CO ratio. The lanthanum in the catalyst LaNi0.9Zr0.1O3 was partially substituted for cerium and zirconium for yttrium to give La0.6Ce0.4Ni0.9Zr0.1−xYxO3 (x = 0.05, 0.07, and 0.09). The La0.6Ce0.4Ni0.9Zr0.1−xYxO3 catalyst’s activity increases with an increase in yttrium loading. The activities of the yttrium-modified catalysts La0.6Ce0.4Ni0.9Zr0.03Y0.07O3 and La0.6Ce0.4Ni0.9Zr0.01Y0.09O3 are higher than the unmodified La0.6Ce0.4Ni0.9Zr0.1O3 catalyst, the latter having methane and carbon dioxide conversion values of 84% and 87%, respectively, and the former with methane and carbon dioxide conversion values of 86% and 90% for La0.6Ce0.4Ni0.9Zr0.03Y0.07O3 and 89% and 91% for La0.6Ce0.4Ni0.9Zr0.01Y0.09O3, respectively. The BET analysis depicted a low surface area of samples ranging from 2 to 9 m2/g. The XRD peaks confirmed the formation of a monoclinic phase of zirconium. The TPR showed that apparent reduction peaks occurred in moderate temperature regions. The TGA curve showed weight loss steps in the range 773 K–973 K, with CsNi0.9Zr0.1O3 carbon deposition being the most severe. The coke deposit on La0.6Ce0.4Ni0.9Zr0.1O3 after 7 h time on stream (TOS) was the lowest, with 20% weight loss. The amount of weight loss increases with a decrease in zirconium loading

In Situ Regeneration of Alumina-Supported Cobalt–Iron Catalysts for Hydrogen Production by Catalytic Methane Decomposition

A novel approach to the in situ regeneration of a spent alumina-supported cobalt&#8315;iron catalyst for catalytic methane decomposition is reported in this work. The spent catalyst was obtained after testing fresh catalyst in catalytic methane decomposition reaction during 90 min. The regeneration evaluated the effect of forced periodic cycling; the cycles of regeneration were performed in situ at 700 &#176;C under diluted O2 gasifying agent (10% O2/N2), followed by inert treatment under N2. The obtained regenerated catalysts at different cycles were tested again in catalytic methane decomposition reaction. Fresh, spent, and spent/regenerated materials were characterized using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), laser Raman spectroscopy (LRS), N2-physisorption, H2-temperature programmed reduction (H2-TPR), thermogravimetric analysis (TGA), and atomic absorption spectroscopy (AAS). The comparison of transmission electron microscope and X-ray powder diffraction characterizations of spent and spent/regenerated catalysts showed the formation of a significant amount of carbon on the surface with a densification of catalyst particles after each catalytic methane decomposition reaction preceded by regeneration. The activity results confirm that the methane decomposition after regeneration cycles leads to a permanent deactivation of catalysts certainly provoked by the coke deposition. Indeed, it is likely that some active iron sites cannot be regenerated totally despite the forced periodic cycling

Response surface methodology for Ni-zeolite catalyst optimization in syngas production

This work addresses the problem of converting waste methane, a significant greenhouse gas, using customized nickel-zeolite catalysts to produce profitable syngas. The investigation employs 5 wt % of Ni on various zeolite supports with Si/Al ratios ranging from 13 to 25. Comprehensive characterization methods, including temperature-programmed reduction, N2 adsorption–desorption, and X-ray diffraction, were used to identify critical structural characteristics that greatly impact the catalyst’s performance. The study indicates that the reducibility and basicity of the catalyst, the type of zeolite support, and the kind of carbon deposits formed during the reaction at 800 °C all influence the efficiency of methane conversion to syngas. The best catalyst was found to be 5Ni-Z3, which at 800 °C produced high conversion rates of carbon dioxide (60%) and methane (50%). Lastly, the response surface methodology, in conjunction with numerical simulation, was used to determine the best operating settings for maximizing syngas production with the 5Ni-Z3 catalyst. Reaction temperature, space velocity, and the methane-to-carbon dioxide feed ratio were considered in this analysis. With a methane conversion rate exceeding 92%, a carbon dioxide conversion rate exceeding 90%, and a hydrogen-to-carbon monoxide ratio of 1.00, the catalyst produced experimental results very similar to the SRM predictions when the reaction was conducted at conditions close to the predicted values [temperature around 845 °C, space velocity around 22,000 mL/(h·gcat), and feed ratio close to 0.94]. The effectiveness of the identified operating conditions for the dry reforming process is validated by the near alignment of expected and experimental outcomes.<br/

Catalytic Performance of Lanthanum Promoted Ni/ZrO2 for Carbon Dioxide Reforming of Methane

Nickel catalysts supported on zirconium oxide and modified by various amounts of lanthanum with 10, 15, and 20 wt.% were synthesized for CO2 reforming of methane. The effect of La2O3 as a promoter on the stability of the catalyst, the amount of carbon formed, and the ratio of H2 to CO were investigated. In this study, we observed that promoting the catalyst with La2O3 enhanced catalyst activities. The conversions of the feed, i.e., methane and carbon dioxide, were in the order 10La2O3 &gt; 15La2O3 &gt; 20La2O3 &gt; 0La2O3, with the highest conversions being about 60% and 70% for both CH4 and CO2 respectively. Brunauer&ndash;Emmett&ndash;Teller (BET) analysis showed that the surface area of the catalysts decreased slightly with increasing La2O3 doping. We observed that 10% La2O3 doping had the highest specific surface area (21.6 m2/g) and the least for the un-promoted sample. The higher surface areas of the promoted samples relative to the reference catalyst is an indication of the concentration of the metals at the mouths of the pores of the support. XRD analysis identified the different phases available, which ranged from NiO species to the monoclinic and tetragonal phases of ZrO2. Temperature programmed reduction (TPR) analysis showed that the addition of La2O3 lowered the activation temperature needed for the promoted catalysts. The structural changes in the morphology of the fresh catalyst were revealed by microscopic analysis. The elemental compositions of the catalyst, synthesized through energy dispersive X-ray analysis, were virtually the same as the calculated amount used for the synthesis. The thermogravimetric analysis (TGA) of spent catalysts showed that the La2O3 loading of 10 wt.% contributed to the gasification of carbon deposits and hence gave about 1% weight-loss after a reaction time of 7.5 h at 700 &deg;C

High carbon-resistant nickel supported on yttria–zirconia catalysts for syngas production by dry reforming of methane: The promoting effect of cesium

Dry reforming of methane (DRM) is a highly researched process for conversion of methane into syngas that consumes the greenhouse gas (CO2). In this work, the promotional effect of cesium on yttria-zirconia-supported nickel catalysts is studied, for the first time, in DRM. Cs loading was varied from 0.5 to 4.0 wt% and fresh materials were characterized by N2 sorption, XRD, TPR, and TEM, while spent catalysts were examined by TEM, Raman spectroscopy, and TGA after catalytic testing. Interestingly, cesium improved carbon resistance of the catalysts. It was shown that addition of up to 1.0 wt% Cs resulted in formation of 13–14 nm nanoparticles in strong interaction with the support, which prevented their sintering during reaction. In this case, hydrogen yield exceeded 75% after 420 min on stream, and this value was higher than those reported in literature for the same loading of other promoters like cerium and barium. However, as the amount of cesium surpassed 1.0 wt%, catalytic performance was lowered, even below that of Cs-free sample and this can be assigned to a possible coverage of active sites by excess cesium. An optimum range of 0.5–1.0 wt% was thus determined for a good performance in dry reforming of methane