scholarly journals Effect of Microwave Drying, Calcination and Aging of Pt/Al2O3 on Platinum Dispersion

Catalysts ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 348 ◽  
Author(s):  
Xavier Auvray ◽  
Anthony Thuault
Keyword(s):  
Microwave Heating ◽  
Single Mode ◽  
Microwave Treatment ◽  
Microwave Drying ◽  
Conventional Heating ◽  
Bet Surface Area ◽  
Great Ability ◽  
Subsequent Calcination ◽  
Platinum Dispersion ◽  
Al2o3 Catalyst

The effect of heating method employed for drying and calcination during the synthesis of 1 wt% Pt/Al2O3 catalyst was investigated. Conventional heating (CH) in resistive oven and microwave heating (MW) in single mode were applied, and the Pt dispersion and Brunauer-Emmett-Teller (BET) surface area were measured to characterize the samples. It was evidenced that the fast and homogeneous heating offered by the microwave heating led to higher Pt dispersion. However, this benefit was only achieved when the subsequent calcination was performed in a conventional oven. The aging in microwave oven of conventionally prepared—as well as MW-prepared—catalysts demonstrated the great ability of microwave irradiation to accelerate platinum sintering. After 1 h at 800 °C under microwave, catalysts showed a dispersion of 5%. Therefore, microwave treatment should be considered for accelerated catalyst aging but should be avoided as a calcination technique for the synthesis of highly dispersed Pt/Al2O3.

Effect of Microwaves on Microorganisms in Foods1,2

1980 ◽  
Vol 43 (8) ◽  
pp. 641-650 ◽  
Author(s):  
DANIEL Y. C. FUNG ◽  
F. E. CUNNINGHAM
Keyword(s):  
Microwave Heating ◽  
Food Systems ◽  
Treatment Time ◽  
Bacterial Species ◽  
Microwave Treatment ◽  
Conventional Heating ◽  
Uniform Heating ◽  
Cereal Products ◽  
Microwave Cooking ◽  
Naturally Occurring

Microwave cooking has increased in popularity in recent years. Since the time to process food is much shorter than with conventional methods, questions have been raised as to the microbial safety of foods cooked with microwaves. The first part of this review includes discussions on the importance of intrinsic and extrinsic characteristics of foods in relation to destruction of microorganisms in microwave-cooked foods, the mechanism of microwave destruction of microorganisms and viewpoints on the thermal and nonthermal destruction of microorganisms. The second part includes data on the effect of time and temperature on microorganisms in microwave-cooked foods, the effect of microwave destruction of microorganisms in different food systems and the effect of microwaves on different bacteria. The last section includes discussions of destruction of microorganisms by microwave cooking of meats, poultry and egg products, dairy products, cereal products, fruit products, vegetables and miscellaneous foods. We observed that (a) microwave heating of food is more “food dependent” than conventional heating, (b) the manufacturer-recommended microwave treatment time for some foods may not destroy high levels of bacteria, (c) use of microwaves in combination with other conventional heating methods results in more uniform heating in foods and destruction of bacteria, (d) heat generated by microwaves kills naturally-occurring microorganisms as long as the size and type of food are carefully correlated with exposure time, (e) microwaves exert different killing effects on individual bacterial species and (f) the question of thermal versus nonthermal effects of microwaves on microorganisms has not been settled. We believe microwave heating is an important method for processing of foods at home, in institutions and in commercial operations. The process is acceptable from the standpoint of food spoilage and food safety as long as the users understand the limitations and possibilities of microwave heating and are aware of some of the major points presented in this review.

Comparing Characteristics of Oil Palm Biochar Using Conventional and Microwave Heating

2014 ◽  
Vol 68 (3) ◽  
Author(s):  
Fatimatul Zaharah Abas ◽  
Farid Nasir Ani
Keyword(s):  
Microwave Heating ◽  
Oil Palm ◽  
Thermal Conversion ◽  
Conventional Heating ◽  
Bet Surface Area ◽  
Slow Heating ◽  
Attractive Alternative ◽  
Pyrolysis Products ◽  
Microwave Pyrolysis

Microwave heating technique is one of the most attractive alternative applications in the thermal conversion process. In addition, microwave pyrolysis is one of the thermochemical technologies using microwave irradiation heating in order to obtain biofuels and materials from biomass. Microwave pyrolysis not only overcomes the disadvantages of conventional pyrolysis methods such as slow heating, but also improves the quality of final pyrolysis products. Recently, the biomass from oil palm wastes (empty fruit bunch, oil palm shell and oil palm fiber) has been gaining more attention in order to produce the biochar. In addition, biochar is important for sequestering carbon and as an effectively additive to improve soil fertility, aid sustainable production, reduce contamination of water streams. This paper focused on the comparison of biochar characteristics produced from oil palm biomass via microwave heating and conventional heating. Analysis on the characteristics of the biochar includes its physical properties, proximate and elemental analysis, the Brunauer- Emmet- Teller (BET) surface area and Scanning Electron Microscopy (SEM).

Preparation of Granular Red Mud Adsorbent using Different Binders by Microwave Pore – Making and Activation Method

2016 ◽  
Vol 35 (4) ◽  
pp. 407-415
Author(s):  
Thiquynhxuan Le ◽  
Hanrui Wang ◽  
Shaohua Ju ◽  
Jinhui Peng ◽  
Liexing Zhou ◽  
...  
Keyword(s):  
Microwave Heating ◽  
Surface Area ◽  
Red Mud ◽  
Heating Temperature ◽  
Holding Time ◽  
Conventional Heating ◽  
Bet Surface Area ◽  
Good Effect ◽  
Optimum Conditions ◽  
Microwave Roasting

AbstractIn this work, microwave energy is used for preparing a granular red mud (GRM) adsorbent made of red mud with different binders, such as starch, sodium silicate and cement. The effects of the preparation parameters, such as binder type, binder addition ratio, microwave heating temperature, microwave power and holding time, on the absorption property of GRM are investigated. The BET surface area, strength, pore structure, XRD and SEM of the GRM absorbent are analyzed. The results show that the microwave roasting has a good effect on pore-making of GRM, especially when using organic binder. Both the BET surface area and the strength of GRM obtained by microwave heating are significantly higher than that by conventional heating. The optimum conditions are obtained as follows: 6:100 (w/w) of starch to red mud ratio, microwave roasting with a power of 2.6 kW at 500℃ for holding time of 30 min. The BET surface area, pore volume and average pore diameter of GRM prepared at the optimum conditions are 15.58 m2/g, 0.0337 cm3/g and 3.1693 A0, respectively.

scholarly journals Microwaves and Heterogeneous Catalysis: A Review on Selected Catalytic Processes

Catalysts ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 246 ◽  
Author(s):  
Vincenzo Palma ◽  
Daniela Barba ◽  
Marta Cortese ◽  
Marco Martino ◽  
Simona Renda ◽  
...  
Keyword(s):  
Heterogeneous Catalysis ◽  
Energy Saving ◽  
Microwave Heating ◽  
Microwave Radiation ◽  
Heterogeneous Catalysts ◽  
Conventional Heating ◽  
Specific Effects ◽  
Natural Choice ◽  
Future Challenges ◽  
Catalyzed Reactions

Since the late 1980s, the scientific community has been attracted to microwave energy as an alternative method of heating, due to the advantages that this technology offers over conventional heating technologies. In fact, differently from these, the microwave heating mechanism is a volumetric process in which heat is generated within the material itself, and, consequently, it can be very rapid and selective. In this way, the microwave-susceptible material can absorb the energy embodied in the microwaves. Application of the microwave heating technique to a chemical process can lead to both a reduction in processing time as well as an increase in the production rate, which is obtained by enhancing the chemical reactions and results in energy saving. The synthesis and sintering of materials by means of microwave radiation has been used for more than 20 years, while, future challenges will be, among others, the development of processes that achieve lower greenhouse gas (e.g., CO2) emissions and discover novel energy-saving catalyzed reactions. A natural choice in such efforts would be the combination of catalysis and microwave radiation. The main aim of this review is to give an overview of microwave applications in the heterogeneous catalysis, including the preparation of catalysts, as well as explore some selected microwave assisted catalytic reactions. The review is divided into three principal topics: (i) introduction to microwave chemistry and microwave materials processing; (ii) description of the loss mechanisms and microwave-specific effects in heterogeneous catalysis; and (iii) applications of microwaves in some selected chemical processes, including the preparation of heterogeneous catalysts.

scholarly journals A comparative study on quality parameters of pumpkin, melon and sunflower oils during thermal treatment

OCL ◽  
2019 ◽  
Vol 26 ◽  
pp. 32 ◽  
Author(s):  
Zhana Petkova ◽  
Ginka Antova
Keyword(s):  
Fatty Acid Composition ◽  
Fatty Acid ◽  
Thermal Treatment ◽  
Microwave Heating ◽  
Acid Composition ◽  
Seed Oil ◽  
Conventional Heating ◽  
Melon Seed ◽  
Sunflower Oils ◽  
Melon Seed Oil

Current paper reveals the impact of thermal treatment on the quality of two seed oils – pumpkin and melon compared to the quality of the most used oil – sunflower oil. Conventional and microwave heating were used for processing the oils. The duration of the thermal treatment was 9, 12 and 18 min for the conventional heating. The microwave heating was performed with two microwave powers of the equipment (600 W and 900 W) for 3, 6, 9 and 12 min. At every stage of the thermal processing were determined acid and peroxide value, the absorbance of the oils at 232 and 268 nm, tocopherol and fatty acid composition. It was observed that the degree of oxidation of the examined oils during microwave and conventional heating increased with the duration of the thermal process and the power of the microwaves. Also, the two methods of heating had a little impact on the processes leading to the formation of free fatty acids. Total tocopherols of the melon seed oil were more stable to thermal treatment. The amount of linoleic acid decreased in the pumpkin and sunflower oils during microwave treatment, while that of oleic and palmitic acid relatively increased. The biggest change in the fatty acid composition of both oils was found during microwave heating at 900W. The changes in fatty acid composition of thermally treated melon seed oil were insignificant. Overall, melon seed oil was observed to be more thermally stable than pumpkin and sunflower oils.

Comparative study of conventional and microwave heating of polyacrylonitrile-based fibres

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Guozhen Zhao ◽  
Jianhua Liu ◽  
Lei Xu ◽  
Shenghui Guo
Keyword(s):  
Microwave Heating ◽  
Surface Defects ◽  
Energy Dispersive Spectrometer ◽  
Xrd Analysis ◽  
Economic Benefits ◽  
Heating Time ◽  
Oxidation Temperature ◽  
Conventional Heating ◽  
Heating Method ◽  
Molecular Arrangement

Abstract The effects of the conventional heating method and the microwave heating method on polyacrylonitrile-based fibres in the temperature range of 180–280 °C were investigated. Fourier transform infrared spectroscopy, X-ray wide-angle scattering, Raman spectroscopy, energy-dispersive spectrometer, scanning electron microscopy and bulk density were used to characterise the properties of the samples. Results show that the microwave heating method can shorten the pre-oxidation time, reduce pre-oxidation temperature and reduce the number of surface defects. The pre-oxidised fibres obtained by the microwave heating method exhibit not only good crystallite size but also a smooth surface. Atomic morphology and molecular arrangement are orderly inside the fibre. The FT-IR spectrum shows that the oxidation reaction occurs at 220 °C, and the CI value of PAN fibers stabilised by microwave heating is the larger than the fibers stabilised by conventional heating. XRD analysis shows that fibers stabilised by microwave heating have low stack domains. The SEM and Raman spectra indicate that hydrogen peroxide can improve the surface finish of the fibers and reduce defects. Microwave heating can reduce the pre-oxidation temperature by about 20 °C and shorten the heating time. The economic benefits of using this method are significantly improved.

Preparation of WC-TiC-Ni3Al-CaF2 functionally graded self-lubricating tool material by microwave sintering and its cutting performance

2020 ◽  
Vol 39 (1) ◽  
pp. 45-53 ◽  
Author(s):  
Siwen Tang ◽  
Rui Wang ◽  
Pengfei Liu ◽  
Qiulin Niu ◽  
Guoqing Yang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Microwave Heating ◽  
Cutting Performance ◽  
Conventional Heating ◽  
Hard Alloys ◽  
Dry Cutting ◽  
Temperature Oxidation ◽  
Lubricating Material ◽  
Heating Technology

AbstractWith the concern of the environment, green dry cutting technology is getting more and more attention and self-lubricating tool technology plays an important role in dry cutting. Due to the demand for high temperature performance of tools during dry cutting process, cemented carbide with Ni3Al as the binder phase has received extensive attention due to its excellent high temperature strength and high temperature oxidation resistance. In this paper, WC-TiC-Ni3Al-CaF2 graded self-lubricating material and tools were prepared by microwave heating method, and its microstructure, mechanical properties and cutting performance were studied. Results show that gradient self-lubricating material can be quickly prepared by microwave heating technology, and the strength is equivalent to that of conventional heating technology. CaF2 not only plays a role in self-lubrication, but also refines the grain of the material. A reasonable gradient design can improve the mechanical properties of the material. When the gradient distribution exponent is n1 = 2, the material has high mechanical properties. Cutting experiments show that the WC-TiC-Ni3Al-CaF2 functional gradient self-lubricating tool has better cutting performance than the homogeneous WC-TiC-Ni3Al hard alloys.

Vitamin B1 and B6 Retention in Milk after Continuous-Flow Microwave and Conventional Heating at High Temperatures

2001 ◽  
Vol 64 (6) ◽  
pp. 890-894 ◽  
Author(s):  
ISABEL SIERRA ◽  
CONCEPCIÓN VIDAL-VALVERDE
Keyword(s):  
High Temperatures ◽  
Continuous Flow ◽  
Vitamin B6 ◽  
Vitamin B1 ◽  
Raw Milk ◽  
Microwave Treatment ◽  
Conventional Heating ◽  
Conventional System ◽  
Tubular Heat Exchanger ◽  
Heating And Cooling

The effect of continuous-flow microwave treatment at high temperatures on the retention of vitamins B1 and B6 in raw milk with different fat content was evaluated. Results were compared with those obtained using a conventional system (tubular heat exchanger) with the same heating and cooling phases. Heat treatment of whole (3.4% fat) and skim (0.5% fat) milk at 90°C produced no losses of vitamin B1 or vitamin B6 (pyridoxamine and pyridoxal). However, at 110 and 120°C, while vitamin B1 content of milk remained constant, pyridoxamine increased (4 to 5% and 9 to 11%, respectively) and pyridoxal decreased (5 to 6% and 9 to 12%, respectively). Under the assayed conditions, no differences were observed between the content of these vitamins in conventionally and continuous-flow microwave-treated milk.

A comparison of mutagenic PhIP and beneficial 8-C-(E-phenylethenyl)quercetin and 6-C-(E-phenylethenyl)quercetin formation under microwave and conventional heating

2018 ◽  
Vol 9 (7) ◽  
pp. 3853-3859 ◽  
Author(s):  
Daming Fan ◽  
Lijie Li ◽  
Nana Zhang ◽  
Yueliang Zhao ◽  
Ka-Wing Cheng ◽  
...  
Keyword(s):  
Microwave Heating ◽  
Conventional Heating

Microwave heating produced less genotoxic PhIP and more human beneficial 6-CEPQ and 8-CEPQ than conventional heating.

Combustion Synthesis of Sr-Substituted LaCo0.4Fe0.6O3 Powders

1992 ◽  
Vol 271 ◽  
Author(s):  
J. J. Kingsley ◽  
L. A. Chick ◽  
G. W. Coffey ◽  
D. E. McCready ◽  
L. R. Pederson
Keyword(s):  
Solid State ◽  
Metal Oxides ◽  
Mixed Oxides ◽  
Electronic Conductivity ◽  
Solid State Reactions ◽  
Bet Surface Area ◽  
Metal Nitrates ◽  
Subsequent Calcination ◽  
Multi Phase ◽  
Sorption Characteristics

ABSTRACTSr-substituted perovskite LaCo0.4Fe0.6O3 is known to have excellent mixed ionic and electronic conductivity and increased O2 sorption characteristics. These perovskites are usually prepared by lengthy solid-state reactions of the component oxides at temperatures near 1150°C, and often produce inhomogeneous, multi-phase powders. Presently, it has been prepared by the calcination of combustion-derived fine mixed oxides at 850°C in 6 hrs. Combustion reactions are carried out using precursor solutions containing the corresponding metal nitrates (oxidizers) and glycine (fuel) at 250°C. The metal oxides produced by this process and subsequent calcination were characterized by XRD, TEM and BET surface area analysis.

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