Performance of NiO doped on alkaline sludge from waste photovoltaic industries for catalytic dry reforming of methane

Alkali sludge (AS) is waste abundantly generated from solar photovoltaic (PV) solar cell industries. Since this potential basic material is still underutilized, a combination with NiO catalyst might greatly influence coke resentence, especially in high-temperature thermochemical reactions (Arora and Prasad, RSC Adv. 6:108,668-108688, 2016). This paper investigated alkaline sludge containing 3CaO-2SiO2 doped with well-known NiO to enhance the dry reforming of methane (DRM) reaction. The wet-impregnation method was used to prepare the xNiO/AS (x = 5-15%) catalysts. Subsequently, all catalysts were tested by using X-ray diffraction (XRD), nitrogen adsorption/desorption (BET), temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed desorption of carbon dioxide (TPD-CO2), field emission scanning electron microscopy (FESEM-EDX), and X-ray photoelectron spectroscopy (XPS). The spent catalysts were analyzed by thermogravimetric analysis (TGA/DTG), transmission electron microscopy (TEM), and temperature-programmed oxidation (TPO). The catalytic performance of xNiO/AS catalysts was investigated in a fixed bed reactor connected with gas chromatography thermal conductivity detector (GC-TCD) at a CH4:CO2 flow rate of 30 mL-1 during a 10-h reaction by following (Shamsuddin et al., Int. J. Energy Res. 45:15,463-15,480, 2021d). For optimization parameters, the effects of NiO concentration (5, 10, and 15%), reaction temperature (700, 750, 800, 850, and 900 °C), catalyst loading (0.1, 0.2, 0.3, 0.4, and 0.5 g), and gas hourly space velocity (GHSV) range from 3000, 6000, 9000, 12,000, and 15,000 h-1 were evaluated. The results showed that physical characteristics such as BET surface area and porosity do not significantly impact NiO percentages of dispersion, whereas chemical characteristics like reducibility are crucial for the catalysts' efficient catalytic activity. Due to the active sites on the catalyst surface being more accessible, increased NiO dispersion resulted in higher reactant conversion. The catalytic performance on various parameters that showed 15%NiO/AS exhibited high reactant conversion up to 98% and 40-60% product selectivity in 700 °C, 0.2 g catalyst loading, and 12,000 h-1 GHSV. According to spent catalyst analyses, the catalyst was stable even after the DRM reaction. Meanwhile, increased reducibility resulted in more and better active site formation on the catalyst. Synergetic effect of efficient NiO as active metal and medium basic sites from AS enhanced DRM catalytic activity and stability with low coke formation.

Investigating the stability of Ni and Fe nanoparticle distribution and the MWCNT structure in the dry reforming of methane

Catalysts based on Ni and Fe nanoparticles deposited selectively on carbon nanotubes were investigated before and after the dry methane reforming. Three catalysts were synthesized and evaluated, varying the concentration of Ni inside and Fe outside the carbon tubes. BET analysis revealed that the acid treatment opened the ends of the nanotubes and resulted in a higher surface area. Transmission electron microscopy (TEM) showed 24 layers with inner diameter ranging from 4 to 6 nm and outer diameter ranging from 16 to 22 nm. Raman spectroscopy confirmed that after calcination at high temperature the structure of the nanotubes was maintained. X-ray diffraction (XRD) analysis of the catalysts confirmed the presence of NiO (2.6-3.2 nm) and Fe2O3 (4.3 nm) crystallites. The catalytic tests presented high activity in dry methane reform (DRM). The catalysts 10Ni@CNT and 10Ni@CNT/5Fe presented conversions of CH4 (63 and 67%) and CO2 (72 and 88%), respectively, at 800 °C, under atmospheric pressure. Analysis after the reaction showed an increasing ratio of ID/IG, which indicates the formation of defects. The Raman analysis showed that even after calcination at high temperatures the structures of the nanotubes were mostly preserved, and TEM images showed that during the reaction, there were formation of nanotubes occurring randomly.

Sustainable routes for acetic acid production: Traditional processes vs a low-carbon, biogas-based strategy

The conversion of biogas, mainly formed of CO₂ and CH₄, into high-value platform chemicals is increasing attention in a context of low-carbon societies. In this new paradigm, acetic acid (AA) is deemed as an interesting product for the chemical industry. Herein we present a fresh overview of the current manufacturing approaches, compared to potential low-carbon alternatives. The use of biogas as primary feedstock to produce acetic acid is an auspicious alternative, representing a step-ahead on carbon-neutral industrial processes. Within the spirit of a circular economy, we propose and analyse a new BIO-strategy with two noteworthy pathways to potentially lower the environmental impact. The generation of syngas via dry reforming (DRM) combined with CO₂ utilisation offers a way to produce acetic acid in a two-step approach (BIO-Indirect route), replacing the conventional, petroleum-derived steam reforming process. The most recent advances on catalyst design and technology are discussed. On the other hand, the BIO-Direct route offers a ground-breaking, atom-efficient way to directly generate acetic acid from biogas. Nevertheless, due to thermodynamic restrictions, the use of plasma technology is needed to directly produce acetic acid. This very promising approach is still in an early stage. Particularly, progress in catalyst design is mandatory to enable low-carbon routes for acetic acid production.

Ni-Co bimetallic catalysts on coconut shell activated carbon prepared using solid-phase method for highly efficient dry reforming of methane

Ni-Co bimetallic catalysts supported on coconut shell activated carbon are synthesized using solid-phase method and investigated for dry reforming of methane, to explore the impact of Ni:Co ratio on the catalyst activity and stability. The catalyst performances are evaluated under the temperature varying from 600 to 900 °C and gas hourly space velocity (GHSV) of 7200 mL/h·g-cat. The characterization results show that metal nanoparticles are produced on the support, and the bimetallic catalyst with an explicit Ni:Co ratio (2:1) is the most beneficial for metal particle dispersion and acquires the minimum particle size of 4.41 nm. The bimetallic catalysts with an explicit Ni:Co ratio of 1:2 and 1:1 exhibit a synergistic effect towards the conversions of CH₄ and CO₂, respectively. The experimental results reveal that the highest CH₄ and CO₂ conversions rise to 94.0% and 97.5% within 12 h at 900 °C on average, respectively, assisted with the two bimetallic catalysts. The intensity of disordered carbon and thermal stability are enhanced with the extension of reforming process, contributing to a long-term catalytic stability. Besides, no obvious carbon deposition is detected, leading to a highly catalytic stability for the bimetallic catalysts.

Ni@ZrO2 yolk-shell catalyst for CO2 methane reforming: Effect of Ni@SiO2 size as the hard-template

This paper reports the usage ratio of TEOS and Zr(OBu)₄ on the formation of Ni@ZrO₂ yolk-shell for dry reforming of methane. From XPS analysis, the ZrO₂ hollow shell texture is demonstrated to be [TEOS]/[Zr(OBu)₄] dependent due to different sizes of SiO₂ produced. It found that an adequate ratio of [TEOS]/[Zr(OBu)₄] improves the catalytic conversion of dry reforming of methane. It (Ni@ZrO₂-SiZr-7.7) shows 90% conversion for CH₄ and 93% for CO₂ at a WHSV of 72,000 mLg_cat^-1h^-1 for 50 h at 800 °C with TOF_CH4 of 8.7 s^-1. It proposed that the changes in surface Si/Zr and gradual interconnecting pores contributed to its activity and stability. These finding's potential to be utilized in other high-temperature reactions.