Missing # inserted in tabular mode

I’m somewhat new to Latex. Right now, I’m stuck with table creation. After searching this and other forums, I didn’t manage to sort this out yet, so I kindly ask for your support. If I missed the answer to thins on some other thread, please apologize me in advance.

Below you’ll find my document’s preamble and the table in question. I tried many approaches both on the table coding and the preamble, but none seemed to work. This code returns the following error:

Missing # inserted in alignment preamble.
to be read again
& l.127 …in{tabularx}{| C{4cm} | C{2cm} | C{2cm} |}
There should be exactly one # between &’s, and an halign or valign is being set up. In this case you had none, so I’ve put one in; maybe this will work.

Looking forward to your support, with kind regards,

documentclass[portuguese,a4paper, 10pt,twoside,fleqn]{article}

usepackage[utf8]{inputenc}
%usepackage[english]{babel,varioref}

usepackage[nottoc]{tocbibind}

usepackage{amsfonts,amsmath,amssymb,amsthm}
usepackage[cdot,squaren]{SIunits}
usepackage{color}
usepackage{emptypage} 
usepackage{fancyhdr}
PassOptionsToPackage{hyphens}{url}usepackage[hidelinks]{hyperref}
usepackage{icomma}
usepackage{setspace}
usepackage{subfig,graphicx}
%usepackage{tweaklist}
usepackage[english,portuges]{babel,varioref}
%usepackage{indentfirst} 
usepackage{fancyhdr}
%usepackage[normalmargins,normalleading]{savetrees}
usepackage{enumitem}
usepackage{cite}
usepackage{multicol,multirow,lipsum}
usepackage[final]{pdfpages}
usepackage[toc,page,header]{appendix}
usepackage{csquotes}
usepackage[official]{eurosym}
usepackage{array}
usepackage{hhline}
usepackage{lipsum}
usepackage{outlines}
usepackage{units}
usepackage[font=small,labelfont=bf]{caption}

usepackage{ftnxtra}
%usepackage{fnpos}
usepackage{stfloats}

usepackage{graphicx}
usepackage{subfig}

usepackage[utf8]{inputenc}
usepackage[T1]{fontenc}
%usepackage{imakeidx}
%makeindex[columns=3, title=Índice Alfabético]

usepackage{indentfirst} 

usepackage{pgfplots}
pgfplotsset{width=10cm,compat=1.9}

addtolength{oddsidemargin}{-1cm}
addtolength{evensidemargin}{-1.5cm}
addtolength{textwidth}{3.cm}
addtolength{topmargin}{-1.5cm}
addtolength{textheight}{3.cm}
setlength{headheight}{15pt}
setlength{parskip}{5pt}
newcolumntype{C}[1]{>{centeringletnewlinearraybackslashhspace{0pt}}m{#1}}

DeclareCaptionFormat{cont}{#1 textit{textbf{(continuação)}}#2#3par}

% Comentários footnote sem númeração

newcommandblfootnote[1]{%
  begingroup
  renewcommandthefootnote{}footnote{#1}%
  addtocounter{footnote}{-1}%
  endgroup
}

begin{document}
%maketitle

input{RDM2021_Trab1_Cover}

%newpage

%Índice
pagenumbering{roman}
tableofcontents
cleardoublepage

% % % % % % % % % % % % % % % % % % % % % % % % % % %
%newpage

pagenumbering{arabic}

begin{table}[h!]
centering
%begin{tabular}{C C C}
begin{tabular}{| C{4cm} | C{2cm} | C{2cm} |}
hline textbf{Gás de Efeito de Estufa} & textbf{Fórmula} & textbf{GWP a 100 anos}
hline textit{Dióxido de carbono} & $CO_2$ & 1 
hline textit{Metano} & $CH_4$ & 25 
hline textit{Óxido Nitroso} & $N_2O$ & 298 
hline textit{Hexafluoreto de Enxofre} & $SF_6$ & 22.800 
hline textit{Trifluormetano} & $CHF_3$ & 14.800 
hline textit{Difluormetano} & $CH_2F_2$ & 675 
hline textit{Tetrafluormetano} & $CF_4$ & 7.390 
hline textit{Hexafluoretano} & $C_2F_6$ & 12.200 
hline textit{Octafluorpropano} & $C_3F_8$ & 8.830 
hline textit{Perfluorbutano} & $C_4F_{10}$ & 8.860 
hline textit{Octafluorciclobutano} & $C_4F_8$ & 10.300 
hline textit{Perfluorpentano} & $C_5F_{12}$ & 13.300 
hline textit{Perfluorhexano} & $C_6F_{14}$ & 9.300 
hline textit{Black Carbon} & - & 900 
hline
end{tabular}   
caption{Valores de $CO_{2-eq}$ para alguns GHG. cite{ref:CO2eq}}
label{Tab:CO2-eq}
end{table}

end{document}