Removal Of Chlorine Research Articles

Low-temperature dechlorination methods for pyrolysis oil of municipal plastic waste

Pyrolysis oil produced from municipal plastic waste can be utilized as fuel and various valuable chemicals as an alternative to petroleum. However, pyrolysis oil usually contains a relatively high concentration of chlorinated compounds, obstructing its utilization in the chemical industry. The present research reveals that pyrolysis oil contains inorganic chlorine and organochlorine compounds, and differentiated approaches should be considered to remove Cl from covalent and ionic chlorine linkages. Transition metal-based ZSM-5 catalysts showed remarkable dechlorination performance via mild C-Cl cracking of 1-chlorooctane and 4-chlorotoluene at 180 °C or below. The neutralization method of mixing pyrolysis oil with an alkaline solution quickly eliminated ionic chlorine from inorganic chlorine compounds, reducing Cl concentrations by up to 70 % at temperature below 40 °C. Based on the different dechlorinating pathways, an ideal combination of these two methods was suggested to enhance chlorine removal efficiency from pyrolysis oil.

Study of an electrochemical system with dual cathodes for the treatment of mariculture wastewater

The salinity properties of mariculture wastewater make it a suitable candidate for electrochemical treatment. In this study, an electro-Fenton synergistic electrocatalytic system was developed using a mixed metal oxide anode, often called Dimensionally Stable Anodes (DSA), and dual cathodes, an iron-carrying activated carbon sheet as the first cathode and a stainless-steel plate as the second cathode, to treat mariculture wastewater. The reaction conditions of the system were investigated and optimized. The chemical oxygen demand (COD) removal rate reached 100 % after 80 min under the optimal conditions: an applied voltage of 3.39 V, a plate spacing of 1.07 cm, and an aeration rate of 34.84 L·h−1. The system effectively removed COD and nitrogen from mariculture wastewater. Analyses using GC–MS, UV–visible spectroscopy, and Fourier-transform infrared spectroscopy showed that the system could degrade macromolecular organic pollutants in the wastewater. Mechanistic studies revealed that active chlorine and hydroxyl radicals play crucial roles in pollutant removal. The dynamic operation study indicated that the optimal operating conditions included a vertical water flow direction through the electrodes, and a flow rate of 10 mL·min−1. The oxidant reuse experiment determined a reflux ratio of 1:1 and a reaction time of 60 min, achieving effluent COD and NH3-N concentrations that met the primary discharge standards. The study on residual chlorine removal showed that the input amount of sodium thiosulfate was 0.36 kg, with a treatment cost of 0.32 yuan per ton of water, and the treated effluent met the discharge standards. These results provide a reference for the industrial application of electrochemical methods in treating mariculture wastewater.

Electrochemical chlorine evolution reaction to improve the desalination of sea sand

Sea sand, a vital sand and gravel resource, is rich in chloride, which causes corrosion of steel reinforcements. This study investigates the effect of the electrochemical chlorine evolution reaction (CER) on the desalination of sea sand. The results indicate that the chlorine removal efficiency (RE) of sea sand increased from 48.76 to 56.40 % under optimal conditions: a current density of 15 mA/cm2, an electrolysis time of 1 min, and a sodium sulphate-supported electrolyte concentration of 0.05 mol/L. After 30 days of resting, the dissolved chlorine content in sea sand was 0.154 %, which was 21.03 % lower than that of the control group. The electrically active chlorine-mediated desalination process demonstrated excellent dechlorination ability, facilitated the transformation of metal and organic chlorine into liquid and gaseous forms, and reduced the slow release of chloride from sea sand. Therefore, CER is expected to be an efficient method for sea sand desalination.

A comprehensive solid-state NMR and theoretical modeling study to reveal the structural evolution of layered yttrium hydroxide upon calcination

Layered rare earth hydroxides (LREHs) are a new family of ion-exchangeable layered metal hydroxides, which have extensive applications in various fields due to the unique properties of rare earth cations in the layered structure and the anion exchange capacity. The transformation of layered metal hydroxides to new layered phases that can be restored through the memory effect is critical for their chemistry and applications. However, the structure details of these new phases such as the coordination environments of rare earth cations/counterions and their evolution as a function of calcination temperature remain unclear to date. Herein, a comprehensive 89Y/35Cl solid-state NMR (ssNMR) and theoretical modeling approach was used to reveal the structural evolution of a representative LREH, namely LYH-Cl, upon calcination. We first identified partial decomposition products of Y3O(OH)5Cl2 and Y(OH)3 during the dehydration stage, then uncovered the preferential removal of hydroxide ions on yttrium sites coordinated with chlorine during the dehydroxylation stage, and finally determined the preferential removal of chlorine exposed to the surface of layers during the dechlorination stage. The coordination environments of Y3+ and Cl− undergo significant changes upon calcination, revealed by ssNMR experiments. These findings thus help us to overcome the obstacles impeding the rational design and synthesis of LREH-based functional materials via memory effect, underscoring the vast potential of ssNMR in deepening the understanding of layered metal hydroxides and related materials.

Removal of Residual Chlorine from Stormwater Using Low-Cost Adsorbents and Phytoremediation

In recent decades, the pollution of water with micropollutants has become an increasing environmental concern. Since 2019, increased stormwater pollution from chlorine-based disinfectants has been recorded due to the COVID-19 pandemic. Runoff from disinfected areas and the residual chlorine present in stormwater are transported to surface water bodies, posing a risk to aquatic flora and fauna. The objectives of this study were (1) to evaluate the efficiency of different low-cost and recyclable filter materials in removing residual chlorine, and (2) to test plants’ ability to reduce residual chlorine concentrations through phytoremediation. Experiments were conducted in the laboratory (column and batch) and in the field (raised garden bed) to assess the efficiency of various filter materials (peat, wood chips, sawdust and the lightweight aggregates) in retaining residual chlorine to be implemented in green infrastructure. The best retainers of chlorine were sawdust (96%) and the LWA Leca (76%). No harmful effects of residual chlorine (changes in growth, color, leaf size, etc.) on plants (Tagetes patula or Pisum savitum) were observed and the residual chlorine in the leachate samples was below the equipment’s detection limit. Our research results will contribute to future studies aiming to remove various micropollutants from stormwater using remediation technologies.

PDDA-modified nanoflower-like BiOCl/MXene hybrid electrode for efficient capacitive deionization dichlorination

Currently, chloride ions in industrial water limits its reuse when extending the circulating water cycle. Therefore, it is necessary to remove Cl− to ensure its effective reuse. Considering the development of new materials for efficient electrochemical chloride removal is a key issue limiting the development of capacitive deionization technology for chlorine removal. In this study, BiOCl was grown in situ on the surface of V-MXene, and then a nanoflower-like BiOCl/MXene composite was synthesized by utilizing the properties of MXene as a structure-directing agent to modulate the morphology, which exhibits superior pore structure and specific capacitance. The poly (diallyl dimethylammonium) (PDDA) modification improved the materials’ specific capacitance and reduced energy consumption for dichlorination. The optimal BMP-10 exhibited superior performance for dichlorination, the maximum dichlorination capacity and rate were 161.64 mg g−1 and 2.20 mg g−1 min−1. We found that MXene has excellent properties for exfoliation and morphology modulation of layered materials. Additionally, the electrical properties have an important influence on the electrochemical removal of chloride ions. Here we successfully synthesized an efficient electrode material with unique morphological structure for CDI dichlorination and provided ideas for structure-directing agents and electrical modulation in material design for electrochemical dichlorination.

Chlorate and Trichloromethane Residues in Bulk Tank Milk Produced in the Republic of Ireland before and after Chlorine was Prohibited as a Cleaning Agent on Farms

In an effort to reduce the occurrence of chlorine derived residues such as chlorate and trichloromethane (TCM) in milk and ultimately in dairy products, ‘chlorine-free’ cleaning of milking equipment became compulsory in the Republic of Ireland (ROI) from January 2021. While data exists on TCM levels in bulk tank milk, little is known about the prominence and typical levels (mg/kg) of chlorate residue in bulk tank milk. To address this, 3625 bulk milk samples were collected from six milk processors and were analysed for chlorate and TCM residues across 2020 and 2021, with 2020 representing a period before chlorine-free cleaning was introduced and 2021 being the period after chlorine removal. In 2020, 15% of the samples analysed had detectable levels of chlorate (0.0020–1.6 mg/kg), but this reduced to 8% in 2021 (0.0020–3.9 mg/kg), following the introduction of ‘chlorine-free’ cleaning. Chlorate and TCM residues have not been totally eliminated because sources of residue other than cleaning chemicals exist, i.e., chlorinated water.

Phosphate-Based Dechlorination of Electrorefiner Salt Waste using a Phosphoric Acid Precursor.

Electrochemical processing of spent nuclear fuel in molten chloride salts results in radioactive salt waste. Chlorine removal from the salt has been identified as an effective and efficient first step in the management of high-level waste. In this work, a simple salt was dechlorinated with a phosphoric acid phosphate precursor, resulting in a glassy dechlorinated product. The dechlorination efficacy was evaluated in air and argon environments. This work serves as an initial step to advance the Technological Readiness Level of H3PO4-based dechlorination step toward implementation of iron phosphate waste forms to immobilize electrochemical fuel reprocessing salt waste streams.

Study of chlorine removal from shredder residue: Thermal dechlorination and water leaching

Shredder residue (SR) is an inevitable waste in the production of steel by scrap melting, and the presence of chlorine is the main responsible for its non-use of energy. This study aimed to remove chlorine from SR by thermal dechlorination and water leaching. Thermal dechlorination was first studied from a PVC sample to evaluate the optimum parameters of temperature, heating rate, residence time and atmosphere (N2 or steam). Under optimal conditions for PVC dechlorination, chlorine removals of 73.7 (N2) and 68.0% (steam) were achieved. Optimal parameters were applied to thermal dechlorination of a Brazilian SR with a chlorine content of 2.12 wt%. Reductions in chlorine content to 0.95 and 0.51 wt% were observed with N2 and steam atmospheres, respectively. In an additional evaluation (conducted also with the Brazilian SR and in order to investigate the reactor rotation effect), it was observed that the reactor rotation does not influence the release of chlorine during the thermal treatment but modifies the granulometry of the produced solid. Samples obtained from this test were subjected to a water leaching study to further reduce the chlorine content. The parameters studied were the type of water (tap and distilled), granulometry and carbonation (contact with CO2) in a total of five washing cycles. Carbonation and use of distilled water achieved the highest chlorine removal resulting in a reduction of chlorine content from 1.13 to 0.45 wt%. The obtained results show directions for chlorine removal aiming at the energetic use of shredder residue.

Study on Optimization of Deep Purification Process Design of Zinc Oxygen Pressure Acid Leaching Solution

According to the characteristics of high impurity content and complex composition of oxygen pressure leaching (OPL) solution of zinc sulfide concentrate, combined with the quality requirements of large plate electrowinning and automatic plate stripping, the advanced purification process of solution was designed. Through the deep purification process consisting of neutralization indium precipitation and low iron purification, high temperature antimony salt nickel and cobalt removal, copper slag chlorine removal, low temperature zinc powder replacement copper and cadmium removal, fine purification, calcium and magnesium removal, the contents of harmful impurities such as iron, indium, copper, cadmium, nickel, cobalt, fluorine and chlorine in the solution are strictly controlled to ensure that the quality of the deeply purified zinc sulfate solution is qualified and can meet the needs of continuous and stable production. The energy-saving effect of advanced purification process is obvious, and the average DC power consumption per ton of electric zinc is 2880kWh, reaching the advanced level of the same industry in China. The good effect of advanced purification process ensures the successful application of OPL and large plate zinc electrowinning, and improves the technology and equipment level of zinc smelting industry, which has important popularization and application value.

Dechlorination of a real plastic waste pyrolysis oil by adsorption with zeolites

The adsorptive dechlorination of a pyrolysis oil coming from real plastic waste was investigated using different Na-zeolites (4A, 13X, and Y) as adsorbents. The dechlorination experiments were performed in a fixed bed trap under inert atmosphere operating at moderate temperatures (< 180 °C). The dechlorination efficiency of the adsorbents was significantly improved by performing a dehydration pre-treatment due to the removal of water molecules physisorbed on the zeolite surface. Among the zeolitic materials tested, 13X zeolite showed the best dechlorination efficiency, which was related to its high content of Lewis acid sites (attributed to the presence of Na+ cations ionically interacting with the zeolite framework), acting as chemisorption sites, as well as the high accessibility of the FAU-zeolitic topology to the Cl-containing compounds. For that sample, a detailed study of the adsorption temperature (from 30 to 180 °C) and time on stream (1–6 h) was further carried out. The maximum chlorine removal efficiency was achieved, reducing the chlorine content of the pyrolysis oil from 421 to 45 ppm, at temperatures of about 150 – 180 °C. Interestingly, under these conditions, thermal or catalytic cracking effects of the zeolite on the feedstock were not observed. However, the study of the time on stream showed that, after 3 h, the chlorine removal efficiency of the zeolite started to decrease. Thus, different regeneration treatments were evaluated proving that, after a combustion at 600 °C, the zeolite recovered its initial dechlorination efficiency. This research reveals the potential of the adsorptive dechlorination process with Na-zeolites to reduce the chlorine content in plastic pyrolysis oils under mild operating conditions.

Removing residual chlorine in water using carbon-based material derived from co-pyrolysis of cotton stalk and desulfurized ash

Herein, an environmentally friendly and low-caste absorbent has been studied to perform with high efficiency and fast removal rate of residual chlorine from wastewater. The chlorine removal absorbent was prepared in situ by co-pyrolysis of desulfurization ash (DA) and cotton stalk (CS) in a tube furnace at 600℃. Compared with CS pyrolysis alone, DA promoted the CS decomposition during co-pyrolysis of DA/CS. The maximum yield of pyrolysis gas was 188 mL/g with 11.33 MJ/Nm3, occurred in the DA/CS blending ratio of 50/100. Moreover, DA also catalyzed the well-developed micropore and mesoporous of cotton-stalk base carbon loaded with DA (CBCDA). The CBCDA with 38.62 wt% DA content had a pore volume of 0.0165 m3/g and a maximum specific surface area of 6.890 m²/g, which 1.96-fold and 1.50-fold higher than that of cotton-stalk base carbon, respectively. The further analysis of adsorption revealed that CaSO3 scattered on the surface of CBCDA fast and efficiently converted hypochlorite ion into chloride ion. The absorbent purified 90.02% residual chlorine from 12 mg/L wastewater within 30 min. Therefore, CBCDA absorbent offers a promising approach for fast and highly efficient purification of residual chlorine in wastewater.

Nonthermal Plasma Synthesis of Metallic Ti Nanocrystals

Nanoscale metallic titanium (Ti) offers unique energetic and biocompatible characteristics for the aerospace and biomedical industries. A rapid and sustainable method to form purified Ti nanocrystals is still in demand due to their high oxygen affinity. Herein, we report the production of highly purified Ti nanoparticles with a nonequilibrium face center cubic (FCC) structure from titanium tetrachloride (TiCl4) via a capacitively coupled plasma (CCP) route. Furthermore, we demonstrate a secondary H2 treatment plasma as an effective strategy to improve the air stability of a thin layer of nanoparticles by further removal of chlorine from the particle surface. Hexagonal and cubic-shaped Ti nanocrystals of high purity were maintained in the air after the secondary H2 plasma treatment. The FCC phase potentially originates from small-sized grains in the initial stage of nucleation inside the plasma environment, which is revealed by a size evolution study with variations of plasma power input.

Synergistic roles of Ru, CeO2, and HZSM-5 in a ternary-active center catalyst for catalytic destruction of dichloromethane

Developing well-qualified industrial catalysts with excellent oxidation ability, selectivity, and resistance is still a challenge for chloroalkane destruction. Herein, we optimized the composition of multi-component catalysts with diverse active sites to adjust their acidic and redox properties for reasonable catalytic performance. The synergy of redox center Ru, activation center CeO2, and acid center HZSM-5 endowed the ternary catalyst Ru/CeO2/HZSM-5 with superior low-temperature activity (30 ∼ 60 °C lower for 50 % conversion), promoted stability and chlorine tolerance (100 % conversion for at least 30 h), and less toxic by-products for dichloromethane (DCM) destruction compared with the binary ones, promising for industrial application under tough conditions (e.g., thermal shock, HCl, H2O). The strong interaction of Ru and CeO2 enhanced the redox property of Ru/CeO2/HZSM-5 and thus promoted the deep oxidation of DCM and intermediates, thereby generating more CO2 and less dechlorinated by-products (e.g., CH3Cl). The synergistic effects of Ru, CeO2, and HZSM-5 facilitated chlorine removal and suppressed the generation of polychlorinated by-products (e.g., CHCl3) over the Ru/CeO2/HZSM-5 catalyst by improving redox capacity and inhibiting reactivity of chlorine. Notably, the introduction of CeO2 weakened the hydrophilicity of Ru and HZSM-5, improving the water resistance of the catalyst. The corresponding monolithic catalyst could achieve complete oxidation of DCM at 400 °C with the total concentration of dioxins measured at 0.026 ng I-TEQ kg−1 after continuous operation at 250 °C for 30 h.

Process optimization and mechanism for removal of high-concentration chlorine from municipal solid waste incineration fly ash washing wastewater by Friedel's salt

Waterwashing is an important pretreatment method for the reuse of municipal solid waste incineration (MSWI) fly ash. However, the presence of high levels of chlorides and small amounts of sulfides in the waterwashing solution makes it difficult to treat and reuse. Therefore, in this study, a calcium sulfate- Friedel's salt precipitation method was used to dechlorinate and desulfurize in the MSWI fly ash washing solution. This paper mainly focused on the chloride removal, and the effects of factors such as reagent ratios, temperature, and reaction time on chloride removal rate and the two-stage dechlorination and desulfurization process were optimized. The experimental results indicated that when the ratio in the first stage was n(Ca):n(Al):n(Cl) = 3:1.5:1, and in the second stage, n(Ca):n(Al):n(Cl) = 8:4:1, a chloride removal rate of up to 90.5% and a sulfide removal rate of over 99.88% could be obtained. The deposited particles were analyzed by using FE-SEM, XRD, and FTIR to investigate their size, morphology, phase composition, and functional groups. The study revealed that excessively high or low reagent ratios could reduce the interlayer spacing of Friedel's salt. Additionally, high temperatures led to the decomposition of Friedel's salt, and the dechlorination efficiency was affected.

Low-temperature catalytic dechlorination of model plastic pyrolytic oil over zeolite catalysts

Catalytic dechlorination of model plastic pyrolytic oil was investigated over different types of zeolites and ion-exchanged 13X zeolites at the low temperatures of 20–120 °C. Among different types of parent zeolites (13X, β, MCM-41), 13X had the highest catalytic dechlorination performance. After ion exchange of 13X with Ag+, its catalytic dechlorination performance was significantly enhanced, and the chlorine removal over Ag-13X reached 97.2 % after reaction for 5 h at 120 °C. The characterization results indicated that the acidity of the zeolite governed its catalytic dechlorination performance, and higher acid amount and stronger acid strength are preferred. Different types of chlorinated compounds followed different dechlorination mechanisms. The primary chlorinated alkanes (e.g., 1-chlorooctane) underwent nucleophilic substitution by the surface –OH groups or H2O to form alcohols and HCl, or dehydrochlorination reaction to produce olefins and HCl, while higher chlorinated alkanes with adjacent hydrogen (e.g., chlorocyclohexane) mainly underwent dehydrochlorination reaction to produce olefins and HCl. Chlorinated aromatics (e.g., chlorobenzene) was removed mainly by physical adsorption. Ag-13X showed good stability, and the chlorine removal still retained 72.1 % after 102 h on stream. After four dechlorination-regeneration cycles, the chlorine removal had only a slight decrease due to the partial collapse of its structure and slight loss of its acid amount.

The Adsorption of 2,4-Dichlorobenzoic Acid on Carbon Nanofibers Produced by Catalytic Pyrolysis of Trichloroethylene and Acetonitrile

In this study, carbon nanofibers were synthesized by the catalytic pyrolysis of trichloroethylene (CNF-Cl) and its mixture with acetonitrile (CNF-Cl-N). The addition of acetonitrile resulted in the incorporation of nitrogen in the CNF (0.33 at%), the removal of chlorine, an increase in oxygen-containing functional groups on the surface (from 1.6 to 3.6 at%), and an increase in the volume of mesopores (from 0.35 to 0.41 cm3·g−1) and macropores (from 0.115 to 0.393 cm3·g−1). The study of 2,4-DCBA adsorption on both CNFs revealed that the adsorption capacity showed dependence with a maximum on the 2,4-DCBA concentration in the solution, which was attributed to the electrostatic interactions of adsorbate with adsorbent at various pHs. The adsorption forces were effective over distances greater than the size of the 2,4-DCBA molecule, indicating volume pore filling. The maximum adsorption capacity occurred at 0.7–1.2 mM and a pH of 3.4 ± 0.1. CNF-Cl-N exhibited lower 2,4-DCBA adsorption than CNF-Cl-N due to its lower specific surface area, lower micropore volume, and higher concentration of oxygen-containing groups on the surface. However, these differences were not significant, suggesting that CNFs produced from both chlorine-containing wastes and their mixtures with nitrogen-containing compounds can be effectively used for water treatment to remove 2,4-DCBA.

Formation and evolution of PVC waste-derived hydrochar

Hydrothermal carbonization (HTC) is an effective method for converting solid waste PVC into multifunctional chlorine-free hydrochar. However, the formation and evolution of hydrochar derived from PVC are not clear. In this study, a combination of ultimate analysis, SEM, BET, FTIR, XPS, and 13C NMR analytical techniques was employed for a comprehensive characterization of the surface morphology and molecular structure of rigid PVC(RPVC)-based hydrochars. The influence of additives on the dechlorination of RPVC and structural evolution was investigated, leading to the establishment of the formation and evolution pathway of hydrochars. The results demonstrate that the CaCO3 filler facilitates dechlorination of RPVC by reacting with HCl and providing an additional channel for HCl diffusion. The chlorine removal rate reaches 96.08% at 280 °C and the residual chlorine in hydrochar is detected primarily on its surface. Prior to dechlorination, RPVC underwent a significant isomerization reaction, resulting in the transformation of hydrochar from long straight-chain alkanes into a polymerized aromatic structure. This transformation led to the formation of hydrochar with a relatively stable core structure and a highly active shell structure. These shell layers primarily contain C-O, CO, and O-CO. This study provides vital information for the design of large-scale processes for handling polyvinyl chloride (PVC)-containing waste and upgrading PVC waste into high-value multifunctional materials.

A green and efficient utilization of refractory cyanide tailings containing inclusion gold by microwave roasting

In order to achieve green and efficient utilization of refractory cyanide tailings, the synergistic effect of chlorinating agent, atmosphere and microwave fields was explored in this paper. As per the thermodynamic calculation results, CaCl2 and O2 were selected as the most appropriate chlorinating agent and atmosphere in the experiment. Compared with cyanide tailings, the dielectric properties of the material after adding CaCl2 were significantly improved, especially at high temperature, the dielectric loss was increased by 31.03 %. The microwave penetration depth of cyanide tailings more stable at different temperatures, only between 5 and 10 cm. The heating time is shortened by 25 %. Under best experimental conditions, the gold recovery and chlorine removal rates achieved 81.87 % and 94.85 %, respectively. The participation of CaCl2 led to the generation of new components with a low melting point in gangue, and the surface pores and cracks of the material increased significantly. Air is the cheapest gas, which contained enough oxygen to oxidatively decompose the CaCl2 and assist in the oxidative destruction of gold inclusions by microwave action. The application of CaCl2 and air accelerates the industrialization process of cyanide tailings recovery and treatment.

Room-Temperature Hydrogen-Sensitive Pt-SnO2 Composite Nanoceramics: Contrasting Roles of Pt Nano-Catalysts Loaded via Two Different Methods

Soluble noble metal salts are widely used for loading noble metals as nano-catalysts in many applications. In this paper, Pt-SnO2 composite nanoceramics were prepared from SnO2 nanoparticles and H2PtCl6 using two Pt loading methods separately: for the solution reduction method, a H2PtCl6 solution was added to a suspension of SnO2 and zinc powder to form Pt on SnO2 nanoparticles, and for the impregnation method, Pt was formed from H2PtCl6 in the course of sintering. Although a series of samples prepared using both Pt loading methods showed a solid response to H2 at room temperature, the ones prepared using the solution reduction method exhibited much better room-temperature hydrogen-sensing characteristics. For two samples of 0.5 wt% Pt and sintered at 825 °C, the response value for the sample prepared using the solution reduction method was 9700 to 1% H2–20% O2-N2, which was much larger than the value of 145 for the sample prepared using the impregnation method. Samples prepared using the two Pt loading methods have similar microstructures characterized via XRD, FESEM, EDS, TEM, and HRTEM. However, the residual chlorine content in those using the impregnation method was higher than those using the solution reduction method according to the analysis. It is proposed that the striking difference in room-temperature hydrogen sensing characteristics among samples prepared using these two different Pt loading methods separately resulted from their different chlorine removal processes. This study demonstrates the importance of a proper method for loading noble metals from their soluble salts as nano-catalysts in many applications.