Zeolite and clay based catalysts for CO2 reforming of methane to syngas: A review

The development of coke and heat resistant catalyst for dry reforming of methane (DRM) is the major bottleneck towards the industrialization and commercialization of the process. Zeolite-based and clay-based catalysts are promising candidates for DRM to produce syngas (CO and H2). The abundance, low cost, excellent properties and environmentally friendly nature of these support materials are an added advantage. Herein, this review entails the recent advances in development of zeolite and clay-based catalysts for DRM. In addition, the review captured a discussion on emerging trends in engineered mesostructured DRM catalysts. Tailoring of their framework configuration, pore architecture, crystals morphology and incorporation of active phases have led to the discovery of novel, robust and high-performance catalysts. Notably, advances recorded in the catalysts synthesis procedures and characterization methods were also highlighted and elaborately discussed. It is expected that this review provide a comprehensive roadmap in the quest for an economically and industrially potent catalyst for syngas production via DRM

Effect of iridium loading on the formation of protonic acid sites over Ir/PtHZSM5

The Ir/Pt-HZSM5 with different iridium loading (0.3-1.0 wt%) was prepared by impregnation of iridium on Pt-HZSM5. The acidic properties of Ir/Pt- HZSM5 were studied by FTIR spectroscopy, while the activity of the catalysts was tested for n-pentane isomerization in a microcatalytic pulse reactor. The IR results of adsorbed 2,6-lutidine showed that all catalysts possessed strong Brönsted and Lewis acid sites in the outgassing at 473 K and below. When Ir/Pt-HZSM5 was heated in hydrogen, protonic acid sites were formed with concomitant decrease of Lewis acid sites. An increase in iridium loading continuously decreased the Lewis and Brönsted acid sites and inhibited the formation of protonic acid sites induced by hydrogen. The formation of protonic acid sites induced by hydrogen was also confirmed by the formation of electron detected by ESR spectroscopy. Additionally for n-pentane isomerization, an increase in iridium loading decreased the yield of isopentane due to the inhibition in the formation of protonic acid sites via hydrogen spillover phenomenon

Optimization of boron dispersion on fibrous-silica-nickel catalyst for enhanced CO2 hydrogenation to methane

There are numerous reports regarding boron-containing catalysts for hydrogen-related reactions from CO2 including dry reforming of methane and methanation. Besides enhancing the productivity, boron also improved nickel activity and stability. However, the detailed mechanistic study, particularly in explaining the starring role of boron in the enhanced reactions, is still lacking. Thus, herein we loaded boron on fibrous-silica-nickel and investigated their physicochemical properties and mechanistic route by means of in-situ FTIR for enhanced CO2 methanation. It was found that the appropriate dispersion of boron surrounds the nickel particles is an important factor to improve the adsorption of CO2 before interacting with split hydrogen atom from the nickel sides to form intermediates which are subsequently dehydrated, and then serial hydrogenation gave the final product of methane. Boron also accelerated the methanation and restricted coke formation. A hybrid approach on optimization via a face-centered central composite design and a response surface methodology showed that reaction using H2/CO2 ratio of 6, GHSV of 10,500 mL g−1 h−1, at 500 °C gave the highest percentage of CH4 of 84.3%. To indicate the error, the predicted values were compared to the experimental values, yielding an accurately minimal error ranging from 0 to 11%. As a result, the empirical models generated for CO2 hydrogenation to methane were reasonably accurate, with all actual values for the confirmation runs fitting within the 94% prediction interval

Microwave irradiation technique for synthesis of zeolite A

Synthesization of Zeolite A from colloidal silica was performed by means of microwave irradiation technique under different conditions and was compared with hydrothermal technique. The molar composition at 1 Al203: 1.96 SiO2: 3.165 Na2O: 128 H2O. X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) were used to characterize zeolite A. XRD results for all samples demonstrated a typical diffraction peak of zeolite A. SEM images show almost no-different in crystal size of zeolite A synthesized by microwave irradiation and hydrothermal technique. Thus, we concluded that crystallization of zeolite A has occurred rapidly by microwave irradiation. Microwave technique is a time and energy saving due to crystallization time and higher heating rate as compared to hydrothermal technique

Gold Photocatalysis in Sustainable Hydrogen Peroxide Generation

Hydrogen peroxide (H2O2) is a mild and green oxidant widely employed in organic syntheses, medical sector, disinfection, pulp bleaching, environmental remediation and biological processes. However, its production via the expensive, multiple steps and energy intensive anthraquinone process renders it less sustainable. Photocatalysis is a viable, sustainable and promising strategy to produce H2O2 from green sources: water and molecular O2. This article presents the key developments of photocatalytic H2O2 production using gold (Au) nanoparticles supported on semiconductor photocatalysts. Several photocatalytic systems containing Au nanoparticles and the roles of Au nanoparticles in enhancing the photocatalytic H2O2 production including increasing the visible light absorption, facilitating the charge carrier separation and transfer, and as a catalytic Au active site are discussed. Factors defining the photocatalytic activity such as the effects of Au particle size and loading, localised surface plasmon resonance, mixed-gold component, and design of photocatalysts are reviewed. Finally, the challenges and prospect for further developments of Au photocatalysis in sustainable H2O2 synthesis as well as other related applications are highlighted

Recovery of gold(III) from an aqueous solution onto a durio zibethinus husk

The recovery of gold(III) ions from an aqueous solution onto a durio zibethinus husk (DZH) was examined after varying pH, contact time, adsorbent dosage, initial Au(III) concentration, and temperature. The functional groups of DZH were analyzed by FTIR and Au(III) recovery onto DZH was verified by FESEM–EDX and XRD analysis. Adsorption equilibrium isotherms and kinetics of the DZH were studied using Freundlich and Langmuir models, as well as pseudo first-order, second-order kinetic and intraparticle diffusion equations. The experimental data obtained with DZH fitted best to the Langmuir isotherm model and exhibited a maximum adsorption capacity (qmax) of 1724 µmol g-1. The data followed the pseudo second-order equation. The activation energy of the adsorption (Ea) was estimated to be 38.5 kJ mol-1. Thermodynamic parameters, such as changes in enthalpy, entropy and Gibbs free energy, showed that the adsorption is exothermic, spontaneous at low temperature, and is a chemisorption process. These results indicate that DZH adsorbs efficiently and could be used as a low-cost alternative for the adsorption of Au(III) in wastewater treatment

Promotive effect of hydrogen in N-Hexane isomerization over Ni/Pthy catalyst

Bifunctional catalyst containing 0.1 wt% Ni and 0.1 wt% Pt supported on HY were prepared by incipient wetness impregnation method. The properties of the catalyst were determined by XRD analysis and pyridine adsorbed FTIR spectroscopy. The catalytic activities were tested on n-hexane isomerization by pulse method in a microcatalytic reactor under atmospheric pressure in the presence of hydrogen or nitrogen carrier gas. XRD result showed the decrease of the crystallinity of PtHY after introduction of 0.1 wt% of Ni. While, the ratio of Lewis to Brønsted acid sites increased after the introduction of Ni on PtHY as evidenced by pyridine adsorbed FTIR spectroscopy. In the presence of hydrogen gas, 0.1 wt% Ni increased the yield of isohexane by about 24 % and decreased the activation energy from 124.1 to 111.2 kJ/mol at the temperature range of 403-423 K. In addition, the activation energy decreased to 48.3 kJ/mol for Ni/PtHY at high temperature range of 478-498 K. The presence of hydrogen as a carrier gas gave a promotive effect on the reaction which led to increase the formation of isohexane and suppress the cracking process. While, the presence of nitrogen as a carrier gas promoted dimerization of nhexane which formed the cracking products

Hydrogen spillover behavior of Zn/HZSM-5 showing catalytically active protonic acid sites in the isomerization of n-pentane

The impregnation of zinc particles into MFI zeolite (HZSM-5) caused the formation of catalytically active protonic acid sites for isomerizing n-pentane in the presence of hydrogen. An infrared (IR) study with preadsorbed pyridine revealed that these protonic acid sites originated from the spillover of molecular hydrogen from the zinc species onto the zeolite surface. The requirements for this spillover effect were further studied by IR spectroscopy of adsorbed ammonia and carbon monoxide. The presence of zinc species in HZSM-5 suggested the exchange of acidic character towards strong Lewis acids rather than Brønsted acid sites. The isomerization of n-pentane over the Zn/HZSM-5 catalyst resulted in high activity and stability and the conversion to iso-pentane depends on the promotive effect of hydrogen as a carrier gas

Hybrid tool for occupational health risk assessment and fugitive emissions control in chemical processes based on the source, path and receptor concept

Fugitive emissions are unavoidable releases that occur continuously throughout a process plant or wherever there are connections or seals between the process fluids and the external environment. The daily exposure of workers to such emissions, typically spread across an entire chemical plant, poses a serious threat to their health and safety. Previous works have focused on assessing the occupational health risks in chemical plants through indexes such as the inherent occupational health index and the integrated inherent safety index. The indexes serve as good proxy indicators for potential sources of occupational hazards (chemicals, process conditions) and process equipment. However, by considering the Source-Path-Receptor (SPR) model, the eventual health risk is also dependent on the path and receptor, where a potential leakage and exposure can occur, respectively. Typically, chemical plants are fitted with controls and mitigation measures known as protection layers (PL) to control hazards. Hence, the occupational health risks in chemical plants due to fugitive emissions require a more holistic methodology for assessment and evaluation. Therefore, a hybrid framework for assessing the occupational health risks from fugitive emissions was developed by adopting and integrating the concepts of source-path-receptor, layers of protection and hierarchy of control. The generic protection layers identified were classified according to the traditional hierarchy of controls. At the source, the protection layers identified were hazard elimination/substitution, inherently safer design, and engineering controls. Next, the maintenance and equipment reliability were identified as PL along the exposure path. Finally, at the receptor, worker-exposure was linked to management systems, procedural safety behaviour and culture. Therefore, the proposed methodology can be used for benchmarking and performance tracking of occupational health risk in a chemical plant over time, as the methodology includes the time-varying parameters of plant maintenance, management system compliance, safety behaviour and culture

Cost–effective microwave rapid synthesis of zeolite NaA for removal of methylene blue

In this study, microwave rapid synthesized NaA (NaAmw) was used to adsorb a methylene blue (MB) from an aqueous solution. The adsorption was optimized under four independent variables including: pH, adsorbent dosage, initial concentration, and ageing time based on central composite design (CCD) with response surface methodology (RSM). A period of 15 min was determined to be the optimum microwave ageing time for the synthesis of NaAmw, which is about sixteen times shorter than using conventional heating technique. An amount of 1.0 g L1 NaAmw demonstrated the optimum dosage for adsorption of 120 mg L1 MB, with predicted adsorption uptake of 53.5 mg g�1, at pH 7 within 1 h of contact time at room temperature. This result approximated the laboratory result, which was 50.7 mg g�1. The experimental data obtained with NaAmw best fits the Langmuir isotherm model and exhibited a maximum adsorption capacity (qmax) of 64.8 mg g�1, and the data followed the first-order kinetic equation. The intraparticle diffusion studies revealed that the adsorption rates were not controlled solely by the diffusion step. Thermodynamic studies showed that the adsorption is endothermic, non-spontaneous in nature, and favor at high temperature. These results confirm that the adsorption process of MB onto NaAmw was controlled by both physisorption and chemisorption. The reusability study shows that the NaAmw was still stable after five cycling runs. These results indicate that NaAmw efficiently adsorbed MB, and could be utilized as a cost-effective alternative adsorbent for removing cationic dyes in the treatment of wastewater