Advances in short contact time catalytic partial oxidation systems for syngas and olefins production

The catalytic partial oxidation (CPO) of natural gas over noble metal catalysts is an attractive way to obtain syngas (CO and H2) which can be employed for downstream processes to produce synthetic fuels. The preliminary conversion of methane to syngas is also interesting in the context of advanced combustion systems with reduced NOx emissions. Several catalysts have been studied for CPO of methane, but Rh-based systems have established as the best performing catalysts in terms of both activity and selectivity. Sulphur poisoning is a tricky issue for industrial processes, leading to catalysts loss of activity. Recently, the presence of sulphur containing compounds naturally occurring in natural gas or added as odorants necessary for safety reasons, was recognized as a serious drawback for the costly Rh catalysts. Indeed, sulphur adversely affects the catalytic performance during catalytic partial oxidation adsorbing onto Rh active sites, causing a (reversible) suppression of their steam reforming activity, with an associated risk of catalyst overheating during CPO autothermal operation. Therefore the development of catalysts that are intrinsically sulphur tolerant and are not readily poisoned by the amounts of sulphur commonly found in natural gas is desirable. On the basis of recent works that have shown that metal phosphide catalysts have promising hydrodesulphurization (HDS) properties due to a higher sulphur tolerance than the correspondent metal based catalysts, in this work, a novel structured Rh catalyst doped with phosphorous and supported on alumina, has been prepared and investigated during the CPO of methane under self-sustained conditions at short contact time in the presence of sulphur. Results were compared with the reference undoped Rh/γAl2O3, showing a significant enhancement of the specific steam reforming reaction rate of P-doped catalyst, and a higher sulphur tolerance. Both the findings were correlated to the presence of phosphorous, whose interaction with Rh improved the metal dispersion on the support and inhibited the strong sulphur adsorption lowering the resulting surface S coverage. Since natural gas may comprise significant amounts of ethane beside methane, the CPO of ethane is also object of study, in the view of a direct use of natural gas as feed at the on-site gas field without separating respective components. The importance of the role of the gas phase chemistry, which was found negligible in the case of CH4 CPO over Rh and Pt catalysts, increases for higher alkanes following the progressive lower stability of the C-H bond, as in the case of CPO of ethane or propane, when large quantities of ethylene can be formed with Pt based catalysts (but not with Rh). However, the literature data available in the field of sulphur poisoning during CPO of higher hydrocarbon is so far scarce and somehow contradictory. Therefore, in the second part of this PhD thesis, the effect of sulphur addition to the feed during the CPO of ethane for syngas production (C2H6/O2=1) has been investigated over more conventional Rh and Pt catalysts supported on a γ-alumina washcoat anchored to honeycomb monoliths. The findings obtained confirmed the previous results on CPO of methane on Rh: sulphur addition resulted in a rapid and reversible poisoning, depending on its concentration. However the adverse impact of sulphur is much larger on Rh than on Pt. Due to the more complex chemistry of ethane, two main effects related to the presence of sulphur during its CPO have been identified: i) the strong inhibition of the hydrogenolysis of ethane to methane occurring on Rh but not on Pt; ii) the progressive inhibition of steam reforming of both the reactant (ethane) and one of the products, ethylene, whose formation in turn increases after the introduction of sulphur. The latter result was also observed for Pt catalyst. Since ethylene is thought to be mainly formed by the homogeneous oxidative dehydrogenation of ethane, this result suggested the possibility to take advantage of selective sulphur poisoning in order to maximize the formation of ethylene. The oxidative catalytic conversion of light alkanes (in particular ethane) to olefins is an attractive solution to obtain ethylene and propylene, the most important building blocks for the polymers industry. The CPO of ethane to ethylene (stoichiometric feed ratio C2H6/O2=2) is characterized by a complicated chemistry which involves both heterogeneous and homogeneous reaction paths, whose contribution and synergy may be strongly alterated by S-poisoning. In the final part of this PhD work, S-poisoning of catalytic steam reforming of C2H6 and C2H4 has been investigated as a strategy to increase the process selectivity and yield to ethylene during the CPO of ethane to ethylene (C2H6/O2=2) over Rh and Pt catalysts. In other words, the possibility to use sulphur as an intentional selective poison of undesired heterogeneous reactions to boost the production of ethylene has been exploited. At the same time, taking advantage of the selective poisoning of sulphur on catalytic reforming paths, an attempt has been done to shed light on the complex interaction of hetero-homogeneous chemistry available in a C2H6 CPO reactor, to understand the contribution of heterogeneous reforming reactions to the overall performance of the reactor

Performance and Stability of Metal (Co, Mn, Cu)-Promoted La₂O₂SO₄ Oxygen Carrier for Chemical Looping Combustion of Methane

Oxygen carrier materials based on La2O2SO4 and promoted by small amounts (1% wt.) of transition metals, namely Co, Mn and Cu, have been synthesized and characterized by means of X-ray diffraction (XRD), Brunauer⁻Emmett⁻Teller (BET), Temperature-programmed reduction/oxidation (TPR/TPO) and thermogravimetry-mass-Fourier transform infrared spectrometry (TG-MS-FTIR) experiments under alternating feeds in order to investigate their potential use for the Chemical Looping Combustion process using either hydrogen or methane as the fuel. The chemical looping reactivity is based on the reversible redox cycle of sulfur from S6+ in La2O2SO4 to S2− in La2O2S and entails a large oxygen storage capacity, but it generally requires high temperatures to proceed, challenging material stability and durability. Herein we demonstrate a remarkable improvement of lattice oxygen availability and activity during the reduction step obtained by cost-effective metal doping in the order Co > Mn > Cu. Notably, the addition of Co or Mn has shown a significant beneficial effect to prevent the decomposition of the oxysulfate releasing SO2, which is identified as the main cause of progressive deactivation for the unpromoted La2O2SO4

Effect of steam on the performance of Ca-based sorbents in calcium looping processes

This study addresses the role of water vapour in Calcium Looping (CaL) cycles, and is based on results of an experimental campaign performed in a lab-scale fluidized bed reactor under operating conditions that are representative of a realistic CaL process. Tests have been designed so as to characterize the effect of steam in either the calcination or the carbonation stages, or in both. A reference limestone has been used, and its CO2 capture capacity, propensity to fragmentation and morphological and microstructural changes have been investigated upon iterated looping cycles. Results are discussed to highlight the role of steam on the course of calcium looping

Electrochemical preparation of nanostructured CeO2-Pt catalysts on Fe-Cr-Al alloy foams for the low-temperature combustion of methanol

Pt-based structured catalysts for the low-temperature combustion of methanol have been prepared by electrochemical methods, using Fe-Cr-Al alloy (Fecralloy) foam supports. Among the strategies investigated, pulsed electrodeposition of Pt nanoparticles from an H2PtCl6solution, followed by cathodic electrodeposition of CeO2thin films from a nitrate bath was the most successful. Pt loading and surface area were measured by ICP-MS and cyclic voltammetry, respectively. Although the presence of a CeO2film decreased the Pt surface area accessible to electrolyte it enhanced the performance of the catalysts towards methanol combustion, without affecting the activation energy of the process, due to the formation of additional active sites along the interface of CeO2-coated Pt nanoparticles

Catalytic combustion of methanol on Pt-Fecralloy foams prepared by electrodeposition

The catalytic combustion of methanol in air under lean dry conditions has been studied using Pt-Fecralloy catalysts. These catalysts were prepared by cathodic electrodeposition of Pt onto commercial 50ppi Fecralloy foams, controlling the noble metal loading through the Pt deposition charge. The catalysts were characterized by SEM and XRD at three different stages (as-prepared, after 2h pretreatment at 600°C in air and after use in methanol combustion) and their Pt surface area was estimated by cyclic voltammetry. In combustion tests, methanol oxidation started at temperatures as low as 80°C, and reached 100% conversion to CO2at temperatures that decreased progressively for Pt loadings increasing from 0.8 to 13mgcm-3. The apparent activation energy of methanol combustion was estimated to be 68-70kJmol-1, independent of the Pt loading of the samples. Repeated combustion cycles converged with SEM, XRD characterization of used catalysts to prove the stability of Pt-Fecralloy, under the conditions employed in the tests

Discordance between Genotypic and Phenotypic Drug Resistance Profiles in Human Immunodeficiency Virus Type 1 Strains Isolated from Peripheral Blood Mononuclear Cells

The aim of the study was to analyze the relationship between genotypic and phenotypic drug resistance profiles of human immunodeficiency virus type 1 (HIV-1) strains isolated from patients during double-analogue nucleoside therapy. A drug-resistant HIV strain was isolated from 20 out of 25 patients, with 16 (64%) subjects carrying a virus with multiple drug resistance mutations. The most frequent resistance mutations were M184V (18 isolates) and M41L (7 isolates). Discordance between the genotypic and phenotypic profile for at least one drug was detected in 16 out of 25 strains. Particularly, eight isolates had a discordant genotypic-phenotypic resistance pattern for two drugs and one isolate had such a pattern for three drugs. A genotypic resistance pattern with a phenotypic sensitivity profile was detected in six isolates (four resistant to zidovudine and two resistant to lamivudine). On the other hand for several strains a genotypic pattern of sensitivity pattern to abacavir (10 strains), didanosine (7 strains), stavudine (3 strains), zidovudine (2 strains), and lamivudine (1 strain) with a phenotypic resistance profile was detected. After a follow-up period of 8 months, an impairment of virological and immunological parameters was detected only in subjects with an HIV-1 isolate with a phenotypic resistance profile in despite of the genotypic results. Predicting resistance phenotype from genotypic data has important limitations. Despite the low number of patients and the short follow-up period, this study suggests that during failing therapy with analogue nucleosides, a phenotypic analysis could be performed in spite of an HIV genotypic sensitivity pattern

HPV vaccination after primary treatment of HPV-related disease across different organ sites: a multidisciplinary comprehensive review and meta-analysis

Objective: To assess evidence on the efficacy of adjuvant human papillomavirus (HPV) vaccination in patients treated for HPV-related disease across different susceptible organ sites. Methods: A systematic review was conducted to identify studies addressing the efficacy of adjuvant HPV vaccination on reducing the risk of recurrence of HPV-related preinvasive diseases. Results were reported as mean differences or pooled odds ratios (OR) with 95% confidence intervals (95% CI). Results: Sixteen studies were identified for the final analysis. Overall, 21,472 patients with cervical dysplasia were included: 4132 (19.2%) received the peri-operative HPV vaccine, while 17,340 (80.8%) underwent surgical treatment alone. The recurrences of CIN 1+ (OR 0.45, 95% CI 0.27 to 0.73; p = 0.001), CIN 2+ (OR 0.33, 95% CI 0.20 to 0.52; p < 0.0001), and CIN 3 (OR 0.28, 95% CI 0.13 to 0.59; p = 0.0009) were lower in the vaccinated than in unvaccinated group. Similarly, adjuvant vaccination reduced the risk of developing anal intraepithelial neoplasia (p = 0.005) and recurrent respiratory papillomatosis (p = 0.004). No differences in anogenital warts and vulvar intraepithelial neoplasia recurrence rate were observed comparing vaccinated and unvaccinated individuals. Conclusions: Adjuvant HPV vaccination is associated with a reduced risk of CIN recurrence, although there are limited data regarding its role in other HPV-related diseases. Further research is warranted to shed more light on the role of HPV vaccination as adjuvant therapy after primary treatment