Hydrogen adsorption of O/N-rich hierarchical carbon scaffold decorated with Ni nanoparticles: Experimental and computational studies

Hierarchical carbon scaffold (HCS) with multi-porous structures, favoring hydrogen diffusion and physisorption is doped with 2–10 wt % Ni for storing hydrogen at ambient temperature. Due to N- and O-rich structure of melamine-formaldehyde resin used as carbon precursor, homogeneous distribution of heteroatoms (N and O) in HCS is achieved. 2 wt % Ni-doped HCS shows the highest hydrogen capacity up to 2.40 wt % H₂ (T = 298 K and p (H₂) = 100 bar) as well as excellent reversibility of 18.25 g H₂/L and 1.25 wt % H₂ (T = 298 K and p (H₂) = 50 bar) and electrical production from PEMFC stack up to 0.7 Wh upon eight cycles. Computations and experiments confirm strong interactions between Ni and heteroatoms, leading to uniform distribution small particles of Ni. This results in enhancing reactive surface area for hydrogen adsorption and preventing agglomeration of Ni nanoparticles upon cycling. Ni K-edge XANES spectra simulated from the optimized structure of Ni-doped N/O-rich carbon using DFT calculations are consistent with the experimental spectra and suggest electron transfer from Ni to hydrogen to form Ni–H bond upon adsorption. Considering low desorption temperature (323 K), not only chemisorbed hydrogen is involved in adsorption mechanisms but also physisorption and spillover of hydrogen.     

Relationships of Sensory Bitterness in Lager Beers to Iso‐α‐Acid Contents

Iso‐α‐acids and their chemically modified variants play a large role in evoking the bitter sensory attributes of lager character, but individual consumers may vary in their perception of bitterness. Sixteen lagers were scored in rank‐rating for bitterness by 14 trained assessors and the concentrations of the six bitter components in these beers were determined by high performance liquid chromatography. Relationships between bitterness intensity and the bitter components were modelled well using partial least square regression with a correlation value of 0.92. When 8 assessors carried out time‐intensity scoring of bitterness, profiles for single products were very different. However, single assessor profiles for multiple products showed qualitative similarities but quantitative differences. That individual assessors perceived bitter characters differently in relation to time has implications for new product development.     

First principles calculations of Hydrogen—Titanium vacancy complexes in SrTiO3

Hydrogen has been reported to serve exclusively as a donor in many oxides, including SrTiO₃. In a perfect crystal, a proton stays near an O atom, forming a strong O–H bond. In the presence of cation vacancies, i.e., Sr vacancy and Ti vacancy, protons prefer to electrically passivate the cation vacancies by forming strong bonds with the O atoms surrounding the vacancy. These result in the formation of nH–V_Sr and nH–V_Ti complexes. Based on first principles density functional calculations, local configurations and vibration signatures of nH–V_Sr complexes and their vibrational signatures have been previously reported [T-Thienprasert et al., Identification of hydrogen defects in SrTiO₃ by first-principles local vibration mode calculations, Physical Review B 85, 125205 (2012)]. Here, we report the computational results for nH–V_Ti complexes and compare the results with infrared measurements reported in the literatures.     

Relationships of Sweetness in Lager to Selected Volatile Congeners

Lager is generally brewed to minimise the final sugar content but despite this can have sweet characters. Such flavour notes have been ascribed to concentrations above flavour thresholds of certain volatile congeners: maltol; 4‐hydroxy‐2,5‐dimethyl‐3(2H)‐furanone (HDMF); 4‐hydroxy‐2(5)‐ethyl‐5(2)‐methyl‐3(2H)‐furanone (HEMF); hydroxymethylfurfural (HMF); diacetyl; and specific esters (ethyl acetate, ethyl caproate, ethyl caprylate, and iso amyl acetate). Relationships between scoring of sweetness in lagers and quantitative data on relevant congeners and ethanol were explored. Lagers (23) were scored for sweetness using rank rating and in 18 lagers ten relevant volatile congeners were quantified by gas chromatography. Relationships between sensory and compositional data were modelled. Multiple linear regression was less successful than partial least squares regression (PLS1) based on four principal factors. Calibration values for r²were 0.70 and 0.77, when ester data was excluded and included, and validation values were 0.56 and 0.45, respectively. Prediction was improved to a validation r²= 0.74 when an artificial neural network was used in modelling with the complete compositional data set. It was concluded that in lagers a range of congeners and ethanol contribute in a complex manner to perceptions of sweetness and the relationship with 4‐hydroxyfuranone derivatives merits revaluation.     

Optimization of biodiesel production from crude palm oil using ultrasonic irradiation assistance and response surface methodology

BACKGROUND: Production of biodiesel from crude palm oil (CPO) with 6 wt% of free fatty acid (FFA) using a low‐frequency ultrasonic irradiation (40 kHz) technique was investigated in the present work. The objective of this study was to determine the relationship between various important parameters of the alkaline catalyzed transesterification process to obtain a high conversion to biodiesel. Response surface methodology (RSM) was used to statistically analyze and optimize the operating parameters of the process. A central composite design (CCD) was adopted to study the effects of the methanol to oil molar ratio, the catalyst concentration, reaction temperature, and irradiation time on conversion to biodiesel. RESULTS: The result from the RSM analysis indicated that the methanol to oil molar ratio, catalyst concentration and irradiation time have the most significant effects on the conversion to biodiesel. Moreover, a coefficient of determination (R²) value of 0.93 shows the fitness of a second‐order model for the present study. Based on this second‐order model, the optimum conditions for alkaline catalyzed transesterification of CPO were found to be a methanol to oil molar ratio of 6.44:1, catalyst concentration 1.25 wt%, reaction temperature 38.44 °C and irradiation time 25.96 min. At the calculated optimum condition, the conversion to biodiesel reached 97.85%. Under these same conditions, the experimental value was 98.02 ± 0.6%. CONCLUSIONS: The mathematical model developed has been proven to adequately describe the range of the experimental parameters studied and provide a statistically accurate prediction of the optimum conversion to biodiesel. Copyright © 2011 Society of Chemical Industry     

Time Intensity Parameters of Sweetness Perceptions in Lager Beers

Lagers are generally brewed to minimise the final sugar content. Residual saccharides, derived from starch, contribute little to sweetness. Despite this, certain lagers exhibit sweet characters. These have not been explored in lagers, but are thought to originate from: maltol; 4‐hydroxy‐2,5‐dimethyl‐3(2H)‐furanone (HDMF); 4‐hydroxy‐2(or 5)‐ethyl‐5(or 2)‐methyl‐3(2H)‐furanone (HEMF); hydroxymethylfurfural (HMF); diacetyl; and certain esters (ethyl acetate, ethyl caproate, ethyl caprylate, and iso amyl acetate). This study used time‐intensity (TI) profiling, employing 13 assessors, to study sweetness in 10 lagers, scored similarly for sweetness in rank rating. Single intensity maxima were obtained with all products and all assessors. Data were analysed using ANOVA of curve parameters and non‐centred and centred principal component analyses (PCA). In ANOVA only the area under curve (A_tot) values differed significantly. However, shape of TI profile, or signature, differed between assessors who could on this basis be divided into two groups. In the multivariate data analyses, non‐centred PCA showed significant differences between lagers, parametric modelling and conventional PCA did not. However TI profile data suggested sweetness intensity perceived over the 120 seconds following ingestion could differ, although differences in scoring in rank rating were not significant.     

Relationships of Overall Estery Aroma Character in Lagers with Volatile Headspace Congener Concentrations

In lager beers the intensity of “estery” aroma character is regarded as an important component of sensory quality, but its origins are somewhat uncertain. Overall “estery” aroma intensity was predicted from capillary gas chromatographic (GC) data following solid phase micro extraction (SPME) of headspaces. Estery character was scored in 23 commercial lagers using rankrating, allowing assessors (13) constant access to a range of appropriate standards. From univariate data analysis, all assessors behaved similarly and lagers fell into three significantly different groups: low (1), high (1) and intermediate (21). The quantification of 36 flavour volatiles by SPME of headspaces was reproducible and principal component analysis explained 91% total variance. Multiple linear regression could utilise only a restricted (26) set of flavour volatiles, whereas partial least square regression, that considered all flavour components, showed significant differences and improved prediction. However, an artificial neural network that could compensate for non‐linearities and interactions in ester perception gave the most robust prediction at R² = 0.88.     

Staling in Two Canned Lager Beers Stored at Different Temperatures — Sensory Analyses and Consumer Ranking

Two canned lagers, lager A (5% abv with late hop character) and lager B (4% abv) stored for 0, 7, 14, 21 and 28 days at 4, 12, 30 and 37°C were scored by trained sensory assessors (10) for liking and stale and related attributes of: cabbagy, cardboard, catty, grainy, honey, leathery, metallic, musty, skunky, and sour. Principal component analysis explained 80% data variance in 3 significant (p < 0.05) and 75% in 4 significant factors for A and B, respectively. In both lagers, aging correlated significantly with stale, cabbagy and musty and in A with metallic and sour and in B with catty and skunky. Partial least squares regression (PLS1) models showed good explanations: stale had regression coefficients of 0.88 (calibration) and 0.84 (validation) for A, and 0.96 and 0.91 respectively, for B; for liking 0.92 and 0.90 for A and 0.96 and 0.93 for B. For both lagers, liking was positively correlated with honey and grainy, and inversely with staling attributes. Lagers from 30°C were ranked for liking by 40 consumers against fresh as a hidden reference. Significant (p = 0.05) ranking of A, but not B, correlated with that of trained assessors.     

Relationship of Sensory Staleness in Two Lagers to Headspace Concentrations of trans‐2‐Nonenal and Three Staling Aldehydes

Key compounds in lager staling include furfural, hexanal, 5‐ hydroxymethyl furfural (5‐HMF), and trans‐2‐nonenal. Quantitative data of headspace concentration in two lagers — one premium at 5% (abv), the other a standard product at 4% (abv) — were obtained by solid phase microextraction (SPME) followed by gas chromatography using a mass selective detector (GCMS). The concentrations of the aldehydes were used to predict overall stale scoring from sensory assessor data, of lagers stored at 4, 12, 30, and 37°C for 7, 14, 21 and 28 days. Concentrations of all four aldehydes increased with time of storage and with higher temperatures. Correlation coefficients for prediction of staleness in the premium lager were similar at 0.81 and 0.84 for partial least square regression (PLS1) and artificial neural network (ANN) modelling respectively, and the latter showed a lower root mean square error (RMS error). For the standard product, the correlation coefficients were 0.72 and 0.86, with ANN showing lower RMS error respectively. In both PLS models, E‐2‐ nonenal had high regression coefficients and 5‐HMF lower coefficients. Furfural and hexanal differed in contributions to the lagers.