Conversion of Lignin to Chemical Intermediates:a Study of Pyrolysis of Kraft Lignin

Experiments of pyrolysis of commercial Kraft lignin have been realized in the 250-550 °C range. Product analyses have been performed by FTIR, GC-MS, EDX analyses. The main goal of the work is to optimize the experiments in terms of liquid yield, reduction of oxygen content in the resulting biochar, and removal of sulfur, found mainly in the gas phase. It has been concluded that the amount of the starting lignin charged in the reactor must be limited to be fully positioned in the heating chamber also during high temperature treatment. Sulfur may be partially removed in the gas phase as H2S and CH3SH mainly, by a pre-treatment at 250 °C. The maximum amount of liquid product, mainly constituted by methoxy- and alkyl-methoxy-phenols, and the maximum solid deoxygenation are both obtained at 550 °C

Ethanol and diethyl ether catalytic conversion over commercial alumina and lanthanum-doped alumina: Reaction paths, catalyst structure and coking

Commercial high-pore-volume alumina and La-doped aluminas have been characterized and tested as catalysts for ethanol conversion to ethylene and diethyl ether and for diethyl ether cracking. In order to go deeper on reaction paths and mechanisms, steady state, TPSR and static experiments in an IR cell were performed. It is established that ethylene forms from ethanol by two parallel ways: i) cracking of ethoxy groups that occurs already at low temperature, and ii) the parallel synthesis and cracking of DEE at intermediate temperatures. Coordination of diethyl ether on Lewis sites represents the first step in its decomposition path. Lewis bonded DEE first cracks to ethoxy species and ethylene gas, while ethoxy species in part crack to a second step to another ethylene gas molecule and in part (only at low temperature) can desorb as gaseous ethanol. Commercial low loading lanthanum-doped alumina contain dispersed La3+-O2 12species mainly interacting with the most reactive defect, edge and corner sites of alumina nanocrystals. At higher loading (4 wt% La2O3) very small LaxOyclusters also appear. Lanthanum doping slightly reduces the number of active sites for ethanol dehydration as well as for DEE cracking, thus reducing catalytic activity, but does not modify significantly selectivities and ethylene yields at high temperature. However, it also considerably reduces the amount of carbonaceous residues formed upon both reactions over the catalyst. Thus, La-doping is proposed as a way to improve the alumina catalyst stability in the process. Catalytic cracking of DEE at 673 K does not represent a good way to remove odorous and dense DEE vapours from air, due to the coproduction of small amounts of acetaldehyde together with ethylene

On the Role of Support in Metallic Heterogeneous Catalysis: A Study of Unsupported Nickel\u2013Cobalt Alloy Nanoparticles in Ethanol Steam Reforming

(Co, Ni) bimetallic nanoparticles have been prepared by reducing Ni and Co chloride solutions with sodium borohydride. The obtained materials have been characterized as cast and/or after annealing by means of XRD, magnetic measurements, IR spectroscopy, FE-SEM and TEM microscopies. The resulting nanomaterials, originally amorphous, crystallize into the cubic structure cF4-Cu as homogeneous (Co, Ni) solid solution alloy and with the additional presence of Boron containing phases due to the residual preparation impurities. The bimetallic nanoparticles are active in ethanol conversion in the presence of steam. For low Boron catalysts, the addition of Nickel to Cobalt nanoparticles improves the catalytic activity in ethanol steam reforming allowing yields as high as 87% at 773 K, at high space velocities (GHSV 324,000 h 121 ). The performances of the catalytic unsupported nanoparticles with a Ni/Co atomic ratio equal to 0.26 appear to be better than those of conventional supported catalysts. The state of Boron impurities affect catalytic activity of bimetallic (Co, Ni) NPs. Carbonaceous materials, such as carbon nanotubes and graphitic carbon, form on the catalyst surface upon reaction. Graphical Abstract: [Figure not available: see fulltext.]

Statistical and Proactive Analysis of an Inter-Laboratory Comparison: The Radiocarbon Dating of the Shroud of Turin.

We review the sampling and results of the radiocarbon dating of the archaeological cloth known as the Shroud of Turin, in the light of recent statistical analyses of both published and raw data. The statistical analyses highlight an inter-laboratory heterogeneity of the means and a monotone spatial variation of the ages of subsamples that suggest the presence of contaminants unevenly removed by the cleaning pretreatments. We consider the significance and overall impact of the statistical analyses on assessing the reliability of the dating results and the design of correct sampling. These analyses suggest that the 1988 radiocarbon dating does not match the current accuracy requirements. Should this be the case, it would be interesting to know the accurate age of the Shroud of Turin. Taking into account the whole body of scientific data, we discuss whether it makes sense to date the Shroud again

A study of Ni/La-Al 2 O 3 catalysts: A competitive system for CO 2 methanation

Ni/La-\u3b3-Al 2 O 3 samples containing 13.6 wt.% Ni and a variable amount of lanthana (0, 4, 14 and 37 wt.%) were prepared by incipient wetness impregnation, using silica-free \u3b3-Al 2 O 3 support. The materials were characterized, as such or after reaction, with XRD, H 2 -TPR, IR, UV\u2013vis-NIR, XPS and FE-SEM techniques. They were tested as catalysts for CO 2 methanation at atmospheric pressure at GHSV 55000 h 121 . The reaction is under kinetic control at T < 650\u2013673 K, while the product mixture is under thermodynamic control above this temperature range. Lanthanum addition strongly increases the activity of Ni/\u3b3-Al 2 O 3 for CO 2 methanation. Methane selectivity is increased to nearly 100% at low temperatures (T < 650 K). The CO 2 methanation reaction on La-doped Ni/\u3b3-Al 2 O 3 occurs with similar activation energies (80 kJ/mol), and with slightly higher reaction order for hydrogen and lower reaction order for CO 2 than those observed for undoped Ni/\u3b3-Al 2 O 3 . Lanthanum acts as a promoter because of the stronger basicity of the lanthana-alumina support allowing stronger adsorption of CO 2 as surface carbonates that can be act as \u201creactant reservoirs\u201d. The Ni/La-alumina catalysts studied here are similarly effective as Ru/alumina catalysts for the selective CO 2 methanation at low temperature and atmospheric pressure

Perceptions of the resident of Santiago de Compostela regarding tourism: effects on hospitality

[Abstract] Santiago de Compostela is one of the best-known pilgrimage routes globally, and it connects many countries in Europe. Its historic center was recognized as a UNESCO World Heritage Site in 1985. This article aims to assess the types and quality of social interaction among residents and visitors (city users) of this particular World Heritage City. Many studies were conducted prior to this one about Santiago. However, most of them have missed some recent approaches to the overtourism phase. The “overtourism” is a phase, which was notorious until 2019. The primary sourcing was assessed by a quantitative study accompanied by a questionnaire responded by 588 residents. The results confirmed that those more exposed to tourism were the most critical of their relationship with the visitor. Thus, we confirm a direct relationship between the intensity of contact with the visitor and the negative perception of tourism. The results are helpful for local and regional planners to implement more collaborative and democratic planning in the tourism sector. This is more relevant to destinations recognized as UNESCO and revealed an overtourism scenario. This new approach is urgent and must be prepared in the ongoing COVID-19 pandemic and a short and long-term perspective

Residents’ Perceptions Regarding the Implementation of a Tourist Tax at a UNESCO World Heritage Site: A Cluster Analysis of Santiago de Compostela (Spain)

[Abstract] Even though the residents’ perceptions on the tourist activity have been thoroughly investigated in the last three decades, there are still few similar studies on destinations that are listed as UNESCOWorld Heritage Sites. The research presented in this article assesses the perception of the residents of the municipality of Santiago de Compostela (Spain) regarding the implementation of a tourist tax. The study is based on 588 residents’ responses to a survey conducted through a questionnaire prepared by the authors. Owing to the exponential increase in the number of visitor arrivals to the city, the implementation of a tourist tax could be one of the strategies deployed to improve the tourist experience. It may also allow for a less negative interaction between residents and tourists. The analysis revealed the existence of three clusters: tax-skeptics, tax-enthusiasts, and tax-reactionaries. The results are consistent with the nature of a mature destination, with most respondents supporting the implementation of a tourist tax that could contribute to improving, amongst other things, the quality of the tourist destination for both visitors and residents

Methanation of carbon dioxide on Ru/Al2O3 and Ni/Al2O3 catalysts at atmospheric pressure: Catalysts activation, behaviour and stability

The methanation of carbon dioxide has been studied over 3% Ru/Al2O3 and 20% Ni/Al2O3 commercial catalysts. Experiments have been performed in diluted conditions in a flow catalytic reactor with a continuous IR detection of products. The data, reported here, confirm that 3% Ru/Al2O3 is an excellent catalyst for CO2 methanation (96% methane yield with no CO coproduction at 573 K at 15,000 h-1 GHSV in excess hydrogen). The performance is better than that of Ni/Al2O3 catalyst. The reaction orders over both catalysts with respect to both hydrogen and CO2 were determined over conditioned catalysts. A conditioning of the Ru/Al2O3 catalyst by reactant gas stream was found to be needed and more effective than conditioning in hydrogen, possibly because water vapour formed during methanation reaction will react to remove chlorine impurities from catalyst surface Conditioned Ru/Al2O3 catalyst was found to retain stable high activity after different shut-down and start-up procedures, thus being possibly applicable in intermittent conditions

Preparation of supported catalysts: A study of the effect of small amounts of silica on Ni/Al2O3 catalysts

Nickel catalysts supported on pure alumina (Puralox) and 5% silica-containing alumina (Siralox) have been prepared, characterized (XRD, UV-vis-NIR, IR, H2-TPR and FE-SEM) and tested. It is confirmed that small amounts of silica hinder the surface area loss of alumina upon calcination, allowing the retention of higher surface areas also when NiO is deposited on the support. Depending on the Ni loading, calcination temperature and on the presence/absence of silica, several species of Ni2+ form on the catalyst: highly dispersed ions, Ni-aluminate defective spinel species and NiO particles. The presence of 5% silica hinders the dispersion of Ni2+ ions and the formation of Ni aluminate phase, and favors the formation of the NiO phase. This is attributed to the competition of silica and nickel oxide for interaction on the most reactive surface sites of alumina. Silica shifts Ni species to less reactive sites where the Ni-alumina interaction is weaker. As result of this, the addition of silica to alumina supports gives rise to more easily reducible Ni catalysts, that become active in ethanol steam reforming at lower temperature