Catalytic Sensor Research Articles

Enhancement on Sensitivity and Stability of Methane Sensor by Increasing Pd Amount and Acid-Assisted Loading

Al2O3 was loaded with different amounts (5 wt%, 10 wt%, and 15 wt%) of Pd via isometric-impregnation. Transmission electron microscopy (TEM) demonstrated that the 15 wt% Pd/Al2O3 has numerous Pd nanoparticles formed on Al2O3. To decrease the hydrolysis rate of Pd(NO3)(2), which could cause the formation of Pd aggregates on Al2O3, determinate concentrations of HNO3 were mixed with the impregnation solution. The measuring results of TEM and Brunauer-Emmett-Teller-specific surface areas revealed that 15 wt% Pd loaded with 10 vol% HNO3 has high dispersion on Al2O3. The influences of the loading amounts of Pd and the acidity of the impregnated solution on the sensitivity and stability of gas sensors were investigated. Catalytic combustion gas sensors based on 15 wt% Pd/Al2O3 prepared from a 10 vol% HNO3-90 vork Pd(NO3)(2) impregnating solution exhibited high responses to methane and strong ability to resist organic silicon.

A High-Performance Three-Dimensional Microheater-Based Catalytic Gas Sensor

We report a high-performance catalytic gas sensor based on a 3-D microheater. Two catalytic gas sensors were fabricated by sol-gel process, respectively based on a 3-D microheater with a concave active membrane and a comparative 2-D microheater with a rectangular active membrane, introducing Pd-Pt as catalytic material. Test results of the sensor response to methane indicate that the output signal (ΔV), sensitivity, and signal-to-noise ratio of the 3-D microheater-based gas sensor were more than twice of those of the 2-D microheater-based gas sensor. Moreover, it had a higher output signal-to-power ratio (ΔV/P).

A Miniaturized Catalytic Gas Sensor for Hydrogen Detection Containing a High Porous Catalytic Layer Formed by Dry Lift-Off

This paper presents a miniaturized catalytic gas sensor for hydrogen detection, based on a sputtered high porous catalytic platinum layer, formed by dry lift off. It provides the possibility to structure these sensitive materials without using any chemicals or solvents. Due to the miniaturized device combined with this porous catalytic layer it is possible to reach a high sensitivity and a low response time [1], which offers other operating modes, e.g. alternating input signal modulation [2]. A new sensor design provides a better controlling of the catalytic temperature, which improves the stability of the catalytic structures. A sensitivity of about 1.8 mV /100 ppm is reached.

Preparation of Pd–Pt Co-Loaded TiO2 Thin Films by Sol-Gel Method for Hydrogen Gas Sensing

Catalytic combustion sensors are widely used for H2 gas sensing because they use a simple sensing mechanism and have high chemical, thermal, and mechanical durability by virtue of their simple structure. In this study, Pd, Pt, and Pd–Pt-loaded TiO2 thin films were prepared. Their respective capabilities as H2 gas combustion sensors were investigated. The TiO2 thin films were prepared using sol-gel method on a glass substrate. Then Pd and/or Pt was loaded on them using photocatalytic deposition. H2 gas sensing was assessed at 300°C by measuring the sample resistance under H2 gas (3–100%) and air flow conditions. A Pd–Pt step-by-step loaded sample showed higher sensitivity than either a Pd or Pt single-loaded sample for H2 concentrations of less than 30 vol%. Scanning transmission electron microscopic (STEM) observation revealed its structure: Pt fine particles deposited selectively on the Pd particles pre-deposited on the TiO2 surface. The large surface area of the catalyst and the synergetic effect of Pd and Pt are expected to contribute to the catalytic activity.

Enhanced sensing performance of catalytic combustion methane sensor by using Pd nanorod/γ-Al 2O 3

Novel metal palladium was loaded on γ-Al 2O 3 using decompression distillation, ultrasonic impregnation, and isometric impregnation. Of these loading methods, isometric impregnation was examined to be the best method for preparing high-performance Pd/Al 2O 3 catalysts. The observation with transmission electron microscopy demonstrated that Pd nanorods were formed on γ-Al 2O 3 for the samples preparing with isometric impregnation. The correlation of the morphology of Pd with the loading time was also investigated: Pd catalysts loaded for 2 and 6 h had the almost same nanorod morphology and relatively uniform size. Nitrogen adsorption and desorption isotherms indicate that Pd nanorods increased the BET-specific surface area of Pd/γ-Al 2O 3. The catalytic combustion gas sensor prepared using Pd/γ-Al 2O 3 via isometric impregnation exhibited high sensitivity to methane as well as fast response and recovery properties.

Best Practices in the Allocation, Commissioning, and Maintenance of Ultrasonic Gas-Leak Detectors

Summary Ultrasonic gas-leak detection (UGLD) is gaining broader acceptance in the oil and gas industry as a means for detecting combustible-gas leaks. UGLD responds to high-pressure leaks by measuring the airborne ultrasound emitted, which when detected by the sensor provides a measure that is proportional to the leak rate. Principal advantages of the technology are that it does not require gas to be transported to the detector and it provides coverage for a relatively large area, up to 20 m in radius, suggesting that UGLD is suitable for detecting gas releases in open, well-ventilated sections of offshore platforms. Despite such advantages, the location criteria and commissioning and routine-maintenance procedures for UGLD are not as well understood as those for conventional gas detectors. A reason might be that UGLD requires the establishment of an ambient ultrasonic background-noise level to decide the alarm level and assist with selection of optimal location, a requirement that has no parallel with point infrared (IR) or catalytic sensors. Location of ultrasonic gas-leak detectors is also based on identifying the potential sources of leaks and taking into account acoustic reflections and interferences caused by continuous or short-time-scale background ultrasonic noise. Such newness might be enough to give some would-be users pause. They may believe that UGLD is for people with high technical competence or that mapping, commissioning, and maintenance are best left to UGLD-equipment manufacturers. Experience by one of the authors of this monograph suggests the contrary. UGLD, for its reliance on ultrasound as a proxy for a gas leak, is a simple concept to understand. Over the course of more than 3,000 installations during the last 10 years, offshore-platform personnel have developed best practices that reduce the time and cost required for installing and commissioning ultrasonic gas monitors and that ease the burden on maintenance. In this report, we examine several of these procedures and highlight the simplicity of installation and maintenance of this method of gas detection.

Preliminary study on catalytic combustion-type sensor for the detection of diesel particulate matter

Catalytic oxidation and sensing of simulated diesel particulate matter (PM), which consists of hexadecane and carbon black as substitutes of soluble organic fraction (SOF) and soot, respectively, were investigated with Ag and Pt catalysts supported on TiO 2 and CeO 2. Supported Ag catalysts were active for soot oxidation at temperatures over about 500 °C, while supported Pt catalysts were almost inactive for the soot oxidation. Toward the oxidation of SOF, on the other hand, supported Pt catalysts were more active than supported Ag catalysts. Catalytic combustion-type sensors coated with those catalysts was fabricated, and their sensing characteristics were evaluated. Because of the difficulty to simulate the real sensing condition of PM, employed in this study was the programmed heating of the sensor on which PM or soot was pre-loaded. The results strongly suggest the possibilities to construct the catalytic combustion-type PM sensor and to selectively detect SOF and soot by the proper selection of the catalytic materials and operation temperatures.

Catalytic gas sensor with single-crystalline silicon heater

A single-crystalline silicon heater used in a catalytic sensor of the pellistor type qualitatively changes the pattern of active gas detection, which is related to a nonlinearity of the current-voltage (I-U) characteristic. The shift of the I-U curve toward lower values of the heater current allows both positive and negative components in the sensor response to be separated as determined by varying the bias voltage at a fixed value of the heater current. Under the action of carbon monoxide, the positive component of the sensor response exhibits a clearly pronounced maximum at a heater current of 28 mA and the height of this peak is proportional to CO concentration in a range of 0.5–2.0 vol %.

ChemInform Abstract: Ionogels, Ionic Liquid Based Hybrid Materials

AbstractReview: 194 refs.

Nanosized perovskite oxide NdFeO 3 as material for a carbon-monoxide catalytic gas sensor

In this paper, research on a CO catalytic gas sensor based on nano-crystalline perovskite oxide NdFeO 3 designed for exhaust gas measurement is presented. Nano-crystalline oxide NdFeO 3 was synthesized by a sol–gel citrate technique. The gas sensing characteristics of this sensor were investigated in the concentration range of CO between 0 and 5 vol.% in air. The influences of C 3 H 8, C 4 H 16 gases, relative humidity and air-flow rate on the cross-sensitivity of the CO sensor were also studied.

Measurement of reaction heats using a polysilicon-based microcalorimetric sensor

Abstract In this work we present a low-cost, low-power, small sample volume microcalorimetric sensor for the measurement of reaction heats. The polysilicon-based microcalorimetric sensor combines several advantages: (i) complementary metal oxide semiconductor technology (CMOS) for future integration; (ii) elements of silicon micromachining (MEMS) to control thermal performance; (iii) heterogeneous catalysts for selective detection and analysis of individual gas compounds; and (iv) microfluidics for optimized control over the reaction conditions. A comprehensive study on the electrical properties of polysilicon thin films as a potential material for temperature monitoring of highly exothermic reactions is presented. Resistive measurements were performed up to 800 °C and a temperature coefficient of resistance (TCR) of 3.24 × 10 −4/°C was derived in the quasi-linear resistive range between 300 and 500 °C. The polysilicon thin film temperature sensors show a good stability. Due to its excellent compatibility with silicon technology and chemical inertness, doped polysilicon thin films can be successfully applied in catalytic microreactors and sensor microsystems at high operating temperatures. We demonstrate the performance of polysilicon sensors by the detection of reaction heats for a model reaction – the catalytic oxidation of propane in air at concentrations in the range of 0.01–0.8 vol.% which is below the low explosion level (LEL) of propane of 2.1% [1]. The sensor exhibits immediate and reversible response upon exposure to propane in air. By choosing a selective catalyst the specificity of the sensor can be tuned to different gases.

The influence of catalytic activity on the response of Pt/SnO 2 gas sensors to carbon monoxide and hydrogen

The article presents the results of research studies on ceramics SnO 2 sensors with Pt catalysts. The role of catalysis in gas sensing mechanisms was investigated. In order to obtain samples with different catalytic activity but with identical Pt loading, the Pt/SnO 2 catalysts were calcined at different temperatures (400–800 °C). Structural analysis of these samples was performed. Among the sensors manufactured with Pt/SnO 2, the highest sensitivity was shown for the sensor obtained with Pt/SnO 2 sample sintered at 800 °C. The correlation between catalytic activity and sensor sensitivity is given.

合金化/脱合金化法による白金板表面へのナノポーラス構造形成

For the application of high-surface-area nanoporous platinum (Pt) to catalytic device, electrodes and sensors, dealloying technique, which can synthesize nanoporous Pt, was combined with surface alloying technique. As a result, nanoporous structure with ligament and pore sizes below 10 nm was successfully fabricated on the Pt plate surface. Cyclic voltammetry in H2SO4 indicated that the nanoporous structure increases the true surface area by 170 times. The approximation by spherical pore model suggested that the nanoporous surface layer has a thickness of 200 nm.

Ionogels, ionic liquid based hybrid materials

The current interest in ionic liquids (ILs) is motivated by some unique properties, such as negligible vapour pressure, thermal stability and non-flammability, combined with high ionic conductivity and wide electrochemical stability window. However, for material applications, there is a challenging need for immobilizing ILs in solid devices, while keeping their specific properties. In this critical review, ionogels are presented as a new class of hybrid materials, in which the properties of the IL are hybridized with those of another component, which may be organic (low molecular weight gelator, (bio)polymer), inorganic (e.g. carbon nanotubes, silica etc.) or hybrid organic-inorganic (e.g. polymer and inorganic fillers). Actually, ILs act as structuring media during the formation of inorganic ionogels, their intrinsic organization and physicochemical properties influencing the building of the solid host network. Conversely, some effects of confinement can modify some properties of the guest IL, even though liquid-like dynamics and ion mobility are preserved. Ionogels, which keep the main properties of ILs except outflow, while allowing easy shaping, considerably enlarge the array of applications of ILs. Thus, they form a promising family of solid electrolyte membranes, which gives access to all-solid devices, a topical industrial challenge in domains such as lithium batteries, fuel cells and dye-sensitized solar cells. Replacing conventional media, organic solvents in lithium batteries or water in proton-exchange-membrane fuel cells (PEMFC), by low-vapour-pressure and non flammable ILs presents major advantages such as improved safety and a higher operating temperature range. Implementation of ILs in separation techniques, where they benefit from huge advantages as well, relies again on the development of supported IL membranes such as ionogels. Moreover, functionalization of ionogels can be achieved both by incorporation of organic functions in the solid matrix, and by encapsulation of molecular species (from metal complexes to enzymes) in the immobilized IL phase, which opens new routes for designing advanced materials, especially (bio)catalytic membranes, sensors and drug release systems (194 references).

Improving the Performance of Catalytic Combustion Type Methane Gas Sensors Using Nanostructure Elements Doped with Rare Earth Cocatalysts

Conventional methane gas sensors based on catalytic combustion have the drawbacks of high working temperature, low thermal stability and small measurement range. To improve their performance, cerium, which possesses high oxygen storage and release ability, was introduced via nanotechnology to prepare Ce-contained nanostructure elements. Three kinds of elements with different carriers: Al2O3, n-Al2O3 and n-Ce-Al2O3 were prepared and separately fabricated (Pt-Pd/Al, Pt-Pd/n-Al, Pt-Pd/n-Ce-Al). The performances of Wheatstone Bridges with three different catalytic elements were tested and compared. The results indicated that the cerium-containing element exhibited better performance than other elements regarding activity, anti-sulfur ability and thermal stability. Moreover, a constant temperature circuit was also applied in this system. The measurement range was extended from 4% to 10% by automatically decreasing the working current in a reasonable range. The maximum error for 0%–10% CH4 was controlled below 5%, which fully meets the measurement requirements.

Micromachined catalytic combustible hydrogen gas sensor

An integrated catalytic combustion H 2 sensor has been fabricated by using MEMS technology. Both the sensing elements and the reference elements could be integrated into the suspended micro heaters connected in a suitable circuit such as a Wheatstone configuration with low power consumption. Two sensitive elements and two reference sensors were integrated together onto a single chip. The size of chip was 5.76 mm 2 and the catalytic combustion sensor showed high response to H 2 at operating voltage of 1 V. The response and recovery times to 1000 ppm H 2 were 0.36 s and 1.29 s, respectively.

High sensitivity and fast response SnO 2 and La-SnO 2 catalytic pellet sensors in detecting volatile organic compounds

The characteristic and effectiveness of pure and modified tin dioxide catalytic pellets as volatile organic compound sensors are discussed. The pure and La-doped SnO 2 thick film sensor pellets exhibited highest sensitivity to ethanol, methanol and acetone vapour at sensing temperature 300 °C. The highest sensitivity towards 500 ppm of ethanol, acetone and methanol was achieved by 5 at.% of La-doped SnO 2 with values of ∼57, ∼55 and ∼59, respectively. The enhancement of the sensitivity of La-doped SnO 2 can be explained by the increase of surface areas; decrease of crystallites sizes and the basicity of the lanthanum dopants. The response times for the developed sensors were about 13–15 s for both pure SnO 2 and La-doped SnO 2 illustrated a fast response sensor that could be used as VOC sensors.

Improving anti-sulfur performance of methane sensors by new vectors and active components

Conventional Pd/ (-Al 2O 3 methane sensors are easily poisoned in a sulfur-containing atmosphere, with a subsequent decrease in sensitivity and the working life of methane sensors. We mainly investigated the effect of nanotechnology and a cerium co-catalyst on the stability and anti-sulfur performance of methane sensors. In our experiment, an anti-sulfur methane sensor was prepared by immersing cerium-containing (-alumina nanometer elements into a Pt-Pd bimetallic nanometer catalyst. The experiment about the sensitivity and stability performance of different catalytic methane sensors indicate that sensitivity, decreased by catalyst sulfur poisoning, is improved significantly by adding cerium to the vector. As well, the long-term operational stability of methane sensors increased significantly.

The performance of nano multicomponent cocatalyst in the improvement of catalytic sensor of methane

Based on the deficiency of catalytic elements in methane sensors such as sintering, activity decrease and surface area reduction at high temperature, three different nano vectors Ce-Zr-Al2O3, Ce-Al2O3, and Zr-Al2O3 were prepared via sol-gel technique in the experiment. BET surface area, catalytic activity and thermal stability were tested and compared. It is found from the experiment that the Ce-doped Al2O3 vector possesses higher catalytic activity than pure Al2O3 vector. Zr-doped Al2O3 vector can enhance the thermal stability of methane sensors. Ce-Zr-Al solid solution can be obtained by the presence of Ce and Zr doped with Al2O3. The reaction activity and thermal stability of catalytic sensors were improved because of the unique synergy effect from Ce-Zr-O. Among the mixed cocatalysts, Ce-Zr-O was reported to be an excellent cocatalyst material. The performance of methane sensors can be improved significantly via the modification of Ce-Zr-Al2O3 vector.

Building output–input function of catalytic combustion sensor to diesel vapor

The leaked diesel oil in engine room of ships volatilizes continuously. When the concentration of volatilized diesel vapor reaches the lower flammability limits, security risks will occur. In order to detect the concentration and alarm the risks, it is necessary to place sensors in engine room. This paper begins with the derivation of formula to calculate the diesel oil volume in different concentration of diesel vapor. Then it determines coefficient of the formula via analysis of the physical and chemical properties and volatilization properties of diesel oil. Experiments are designed to obtain the sensitive date to derive the function between sensor output and diesel volume. Then the fitting curve and analysis of linearity are given, and the results show that catalytic combustion sensor can meet the design requirements. In the end, it gives the application of catalytic combustion sensor using in diesel vapor detection and alarm system in engine room.